The labors of coralline zoophytes, as thus observed, form masses of

coral, such as are found fossilized in the strata of the earth. But

our knowledge of the laws of life which have probably affected the

distribution of marine remains in strata, has received other very

striking accessions by the labors of Prof. Edward Forbes in

observing the marine animals of the Ægean Sea. He found that, even

in their living state, the mollusks and zoophytes are already

distributed into strata. Dividing the depth into eight regions, from

2 to 230 fathoms, he found that each region had its peculiar

inhabitants, which disappeared speedily either in ascending or in

descending. The zero of animal life appeared to occur at about 300

fathoms. This curious result bears in various ways upon geology. Mr.

Forbes himself has given an example of the mode in which it may be

applied, by determining the depth at which the submarine eruption

took place which produced the volcanic isle of Neokaimeni in 1707.

By an examination of the fossils embedded in the pumice, he showed

that it came from the fourth region.[68\18]

[Note 68\18: _British Assoc. Reports_, 1843, p. 177.]

To the modes in which organized beings operate in producing the

materials of the earth, we must add those pointed out by the

extraordinary microscopic discoveries of Professor Ehrenberg. It

appears that whole beds of earthy matter consist of the cases of

certain infusoria, the remains of these creatures being accumulated

in numbers which it confounds our thoughts to contemplate.]

Speculations concerning the _causes_ of volcanoes and earthquakes,

and of the rising and sinking of land, are a highly important

portion of this science, at least as far as the calculation of the

possible results of definite causes is concerned. But the various

hypotheses which have been propounded on this subject can hardly be

considered as sufficiently matured for such calculation. A mass of

matter in a state of igneous fusion, extending to the centre of the

earth, even if we make such an hypothesis, requires some additional

cause to produce eruption. The supposition that this fire may be

produced by intense chemical action between combining elements,

requires further, not only some agency to bring together such

elements, but some reason why {554} they should be originally

separate. And if any other causes have been suggested, as

electricity or magnetism, this has been done so vaguely as to elude

all possibility of rigorous deduction from the hypothesis. The

doctrine of a Central Heat, however, has occupied so considerable a

place in theoretical geology, that it ought undoubtedly to form an

article in geological dynamics.

_Sect._ 4.--_The Doctrine of Central Heat._

THE early geological theorists who, like Leibnitz and Buffon,

assumed that the earth was originally a mass in a state of igneous

fusion, naturally went on to deduce from this hypothesis, that the

crust consolidated and cooled before the interior, and that there

might still remain a central heat, capable of producing many

important effects. But it is in more recent times that we have

measures of such effects, and calculations which we can compare with

measures. It was found, as we have said, that in descending below

the surface of the earth, the temperature of its materials

increased. Now it followed from Fourier's mathematical

investigations of the distribution of heat in the earth, that if

there be no primitive heat (_chaleur d'origine_), the temperature,

when we descend below the crust, will be constant in each vertical

line. Hence an observed increase of temperature in descending,

appeared to point out a central heat resulting from some cause now

no longer in action.

The doctrine of a central heat has usually been combined with the

supposition of a central igneous fluidity; for the heat in the

neighborhood of the centre must be very intense, according to any

law of its increase in descending which is consistent with known

principles. But to this central fluidity it has been objected that

such a fluid must be in constant circulation by the cooling of its

exterior. Mr. Daniell found this to be the case in all fused metals.

It has also been objected that there must be, in such a central

fluid, _tides_ produced by the moon and sun; but this inference

would require several additional suppositions and calculations to

give it a precise form.

Again, the supposition of a central heat of the earth, considered as

the effect of a more ancient state of its mass, appeared to indicate

that its cooling must still be going on. But if this were so, the

earth might contract, as most bodies do when they cool; and this

contraction might lead to mechanical results, as the shortening of

the day. Laplace satisfied himself, by reference to ancient

astronomical records, that no such {555} alteration in the length of

the day had taken place, even to the amount of one two-hundredth of

a second; and thus, there was here no confirmation of the hypothesis

of a primitive heat of the earth.

Though we find no evidence of the secular contraction of the earth

in the observations with which astronomy deals, there are some

geological facts which at first appear to point to the reality of a

refrigeration within geological periods; as the existence of the

remains of plants and shells of tropical climates, in the strata of

countries which are now near to or within the frigid zones. These

facts, however, have given rise to theories of the changes of

climate, which we must consider separately.

But we may notice, as connected with the doctrine of central heat,

the manner in which this hypothesis has been applied to explain

volcanic and geological phenomena. It does not enter into my plan,

to consider explanations in which this central heat is supposed to

give rise to an expansive force,[69\18] without any distinct

reference to known physical laws. But we may notice; as more likely

to become useful materials of the science now before us, such

speculations as those of Mr. Babbage; in which he combines the

doctrine of central heat with other physical laws;[70\18] as, that

solid rocks _expand_ by being heated, but that clay contracts; that

different rocks and strata _conduct_ heat differently; that the

earth _radiates_ heat differently, or at different parts of its

surface, according as it is covered with forests, with mountains,

with deserts, or with water. These principles, applied to large

masses, such as those which constitute the crust of the earth, might

give rise to changes as great as any which geology discloses. For

example: when the bed of a sea is covered by a thick deposit of new

matter worn from the shores, the strata below the bed, being

protected by a bad conductor of heat, will be heated, and, being

heated, maybe expanded; or, as Sir J. Herschel has observed, may

produce explosion by the conversion of their moisture into steam.

Such speculations, when founded on real data and sound calculations,

may hereafter be of material use in geology.

[Note 69\18: Scrope _On Volcanoes_, p. 192.]

[Note 70\18: _On the Temple of Serapis_, 1834. See also _Journal of

the Royal Inst._ vol. ii., quoted in Conyb. and Ph. p. xv. Lyell,

B. ii. c. xix. p. 383, (4th ed.) on Expansion of Stone.]

The doctrine of central heat and fluidity has been rejected by some

eminent philosophers. Mr. Lyell's reasons for this rejection belong

{556} rather to Theoretical Geology; but I may here notice M.

**Poisson's opinion. He does not assent to the conclusion of Fourier,

that once the temperature increases in descending, there must be some

primitive central heat. On the contrary, he considers that such an

increase may arise from this;--that the earth, at some former period,

passed (by the motion of the solar system in the universe,) **through

a portion of space which was warmer than the space in which it now

revolves (by reason, it may be, of the heat of other stars to which it

was then nearer). He supposes that, since such a period, the surface

has cooled down by the influence of the surrounding circumstances;

while the interior, for a certain unknown depth, retains the trace of

the former elevation of temperature. But this assumption is not likely

to expel the belief is the terrestrial origin of the subterraneous

heat. For the supposition of such an inequality in the temperature of

the different regions in which the solar system is placed at different

times, is altogether arbitrary; and, if pushed to the amount to which

it must be carried, in order to account for the phenomenon, is highly

improbable.[71\18] The doctrine of central heat, on the other hand,

(which need not be conceived as implying the _universal_ fluidity of

the mass,) is not only naturally suggested by the subterraneous

increase of temperatures, but explains the spheroidal figure of the

earth; and falls in with almost any theory which can be devised, of

volcanoes, earthquakes, and great geological changes.

[Note 71\18: For this hypothesis would make it necessary to suppose

that the earth has, at some former period, derived from some other

star or stars more heat than she now derives from the sun. But this

would imply, as highly probable, that at some period some other star

or stars must have produced also a _mechanical_ effect upon the

solar system, greater than the effect of the sun. Now such a past

operation of forces, fitted to obliterate all order and symmetry, is

quite inconsistent with the simple, regular, and symmetrical

relation which the whole solar system, as far as Uranus, bears to

the present central body.]

_Sect._ 5.--_Problems respecting Elevations and Crystalline Forces._

OTHER problems respecting the forces by which great masses of the

earth's crust have been displaced, have also been solved by various

mathematicians. It has been maintained by Von Buch that there occur,

in various places, _craters of elevation_; that is, mountain-masses

resembling the craters of volcanoes, but really produced by an

expansive force from below, bursting an aperture through horizontal

strata, {557} and elevating them in a conical form. Against this

doctrine, as exemplified in the most noted instances, strong

arguments have been adduced by other geologists. Yet the protrusion

of fused rock by subterraneous forces upon a large scale is not

denied: and how far the examples of such operations may, in any

cases, be termed craters of elevation, must be considered as a

question not yet decided. On the supposition of the truth of Von

Buch's doctrine, M. de Beaumont has calculated the relations of

position, the fissures, &c., which would arise. And Mr.

Hopkins,[72\18] of Cambridge, has investigated in a much more

general manner, upon mechanical principles, the laws of the

elevations, fissures, faults, veins, and other phenomena which would

result from an elevatory force, acting simultaneously at every point

beneath extensive portions of the crust of the earth. An application

of mathematical reasoning to the illustration of the phenomena of

veins had before been made in Germany by Schmidt and

Zimmerman.[73\18] The conclusion which Mr. Hopkins has obtained,

respecting the two sets of fissures, at right angles to each other,

which would in general be produced by such forces as he supposes,

may suggest interesting points of examination respecting the

geological phenomena of fissured districts.

[Note 72\18: _Trans. Camb. Phil. Soc._ vol. vi. 1836.]

[Note 73\18: _Phil. Mag._ July, 1836, p. 2.]

[2nd Ed.] [The theory of craters of elevation probably errs rather

by making the elevation of a point into a particular class of

volcanic agency, than by giving volcanic agency too great a power of

elevation.

A mature consideration of the subject will make us hesitate to

ascribe much value to the labors of those writers who have applied

mathematical reasoning to geological questions. Such reasoning, when

it is carried to the extent which requires symbolical processes, has

always been, I conceive, a source, not of knowledge, but of error,

and confusion; for in such applications the real questions are

slurred over in the hypothetical assumptions of the mathematician,

while the calculation misleads its followers by a false aspect of

demonstration. All symbolical reasonings concerning the fissures of

a semi-rigid mass produced by elevatory or other forces, appear to

me to have turned out valueless. At the same time it cannot be too

strongly borne in mind, that mathematical and mechanical habits of

thought are requisite to all clear thinking on such subjects.]

Other forces, still more secure in their nature and laws, have

played a very important part in the formation of the earth's crust.

I speak of the forces by which the crystalline, slaty, and jointed

structure of {558} mineral masses has been produced. These forces

are probably identical, on the one hand, with the cohesive forces

from which rocks derive their solidity and their physical

properties; while, on the other hand, they are closely connected

with the forces of chemical attraction. No attempts, of any lucid

and hopeful kind, have yet been made to bring such forces under

definite mechanical conceptions: and perhaps mineralogy, to which

science, as the point of junction of chemistry and crystallography,

such attempts would belong, is hardly yet ripe for such

speculations. But when we look at the universal prevalence of

crystalline forms and cleavages, at the extent of the phenomena of

slaty cleavage, and at the _segregation_ of special minerals into

veins and nodules, which has taken place in some unknown manner, we

cannot doubt that the forces of which we now speak have acted very

widely and energetically. Any elucidation of their nature would be

an important step in Geological Dynamics.

[2nd Ed.] [A point of Geological Dynamics of great importance is, the

change which rocks undergo in structure after they are deposited,

either by the action of subterraneous heat, or by the influence of

crystalline or other corpuscular forces. By such agencies, sedimentary

rocks may be converted into crystalline, the traces of organic fossils

may be obliterated, a slaty cleavage may be produced, and other like

effects. The possibility of such changes was urged by Dr. Hutton in

his Theory; and Sir James Hall's very instructive and striking

experiments were made for the purpose of illustrating this theory. In

these experiments, powdered chalk was, by the application of heat

under pressure, converted into crystalline calcspar. Afterwards Dr.

McCulloch's labors had an important influence in satisfying geologists

of the reality of corresponding changes in nature. Dr. McCulloch, by

his very lively and copious descriptions of volcanic regions, by his

representations of them, by his classification of igneous rocks, and

his comprehensive views of the phenomena which they exhibit, probably

was the means of converting many geologists from the Wernerian

opinions.

Rocks which have undergone changes since they were deposited are

termed by Mr. Lyell _metamorphic_. The great extent of metamorphic

rock changed by heat is now uncontested. The internal changes which

are produced by the crystalline forces of mountain masses have been

the subjects of important and comprehensive speculations by

Professor Sedgwick.] {559}

_Sect._ 6.--_Theories of Changes of Climate._

AS we have already stated, Geology offers to us strong evidence that

the climate of the ancient periods of the earth's history was hotter

than that which now exists in the same countries. This, and other

circumstances, have led geologists to the investigation of the

effects of any hypothetical causes of such changes of condition in

respect of heat.

The love of the contemplation of geometrical symmetry, as well as

other reasons, suggested the hypothesis that the earth's axis had

originally no obliquity, but was perpendicular to the equator. Such

a construction of the world had been thought of before the time of

Milton,[74\18] as what might be supposed to have existed when man

was expelled from Paradise; and Burnet, in his _Sacred Theory of the

Earth_ (1690), adopted this notion of the paradisiacal condition of

the globe:

The spring

Perpetual smiled on earth with verdant flowers,

Equal in days and nights.

[Note 74\18: Some said he bade his angels turn askance

The poles of earth twice ten degrees and more

From the sun's axle, &c.--_Paradise Lost_, x. 214.]

In modern times, too, some persons have been disposed to adopt this

hypothesis, because they have conceived that the present polar

distribution of light is inconsistent with the production of the

fossil plants which are found in those regions,[75\18] even if we

could, in some other way, account for the change of temperature. But

this alteration in the axes of a revolution could not take place

without a subversion of the equilibrium of the surface, such as does

not appear to have occurred; and the change has of late been

generally declared impossible by physical astronomers.

[Note 75\18: Lyell, i. 155. Lindley, _Fossil Flora_.]

The effects of other astronomical changes have been calculated by

Sir John Herschel. He has examined, for instance, the thermotical

consequences of the diminution of the eccentricity of the earth's

orbit, which has been going on for ages beyond the records of

history. He finds[76\18] that, on this account, the annual effect of

solar radiation would increase as we go back to remoter periods of

the past; but (probably at least) not in a degree sufficient to

account for the apparent past {560} changes of climate. He finds,

however, that though the effect of this change on the mean

temperature of the year may be small, the effect on the extreme

temperature of the seasons will be much more considerable; "so as to

produce alternately, in the same latitude of either hemisphere, a

perpetual spring, or the extreme vicissitudes of a burning summer

and a rigorous winter."[77\18]

[Note 76\18: _Geol. Trans._ vol. iii. p. 295.]

[Note 77\18: _Geol. Trans._ vol. iii. p. 298.]

Mr. Lyell has traced the consequences of another hypothesis on this

subject, which appears at first sight to promise no very striking

results, but which yet is found, upon examination, to involve

adequate causes of very great changes: I refer to the supposed

various distribution of land and water at different periods of the

earth's history. If the land were all gathered into the neighborhood

of the poles, it would become the seat of constant ice and snow, and

would thus very greatly reduce the temperature of the whole surface

of the globe. If, on the other hand, the polar regions were

principally water, while the tropics were occupied with a belt of

land, there would be no part of the earth's surface on which the

frost could fasten a firm hold, while the torrid zone would act like

a furnace to heat the whole. And, supposing a cycle of terrestrial

changes in which these conditions should succeed each other, the

winter and summer of this "great year" might differ much more than

the elevated temperature which we are led to ascribe to former

periods of the globe, can be judged to have differed from the

present state of things.

The ingenuity and plausibility of this theory cannot be doubted: and

perhaps its results may hereafter be found not quite out of the

reach of calculation. Some progress has already been made in

calculating the movement of heat into, through, and out of the

earth; but when we add to this the effects of the currents of the

ocean and the atmosphere, the problem, thus involving so many

thermotical and atmological laws, operating under complex

conditions, is undoubtedly one of extreme difficulty. Still, it is

something, in this as in all cases, to have the problem even stated;

and none of the elements of the solution appears to be of such a

nature that we need allow ourselves to yield to despair, respecting

the possibility of dealing with it in a useful manner, as our

knowledge becomes more complete and definite. {561}

CHAPTER VI.

PROGRESS OF THE GEOLOGICAL DYNAMICS OF ORGANIZED BEINGS.

_Sect._ 1.--_Objects of this Science._

PERHAPS in extending the term _Geological Dynamics_ to the causes of

changes in organized beings, I shall be thought to be employing a

forced and inconvenient phraseology. But it will be found that, in

order to treat geology in a truly scientific manner, we must bring

together all the classes of speculations concerning known causes of

change; and the Organic Dynamics of Geology, or of Geography, if the

reader prefers the word, appears not an inappropriate phrase for one

part of this body of researches.

As has already been said, the species of plants and animals which

are found embedded in the strata of the earth, are not only

different from those which now live in the same regions, but, for

the most part, different from any now existing on the face of the

earth. The remains which we discover imply a past state of things

different from that which now prevails; they imply also that the

whole organic creation has been renewed, and that this renewal has

taken place several times. Such extraordinary general facts have

naturally put in activity very bold speculations.

But it has already been said, we cannot speculate upon such facts in

the past history of the globe, without taking a large survey of its

present condition. Does the present animal and vegetable population

differ from the past, in the same way in which the products of one

region of the existing earth differ from those of another? Can the

creation and diffusion of the fossil species be explained in the

same manner as the creation and diffusion of the creatures among

which we live? And these questions lead us onwards another step, to

ask,--What _are_ the laws by which the plants and animals of

different parts of the earth differ? What was the manner in which

they were originally diffused?--Thus we have to include, as portions

of our subject, {562} the _Geography of Plants_, and _of Animals_,

and the _History of their change and diffusion_; intending by the

latter subject, of course, _palætiological_ history,--the

examination of the causes of what has occurred, and the inference of

past events, from what we know of causes.

It is unnecessary for me to give at any length a statement of the

problems which are included in these branches of science, or of the

progress which has been made in them; since Mr. Lyell, in his

_Principles of Geology_, has treated these subjects in a very able

manner, and in the same point of view in which I am thus led to

consider them. I will only briefly refer to some points, availing

myself of his labors and his ideas.

_Sect._ 2.--_Geography of Plants and Animals._

WITH regard both to plants and animals, it appears,[78\18] that

besides such differences in the products of different regions as we

may naturally suppose to be occasioned by climate and other external

causes; an examination of the whole organic population of the globe

leads us to consider the earth as divided into _provinces_, each

province being occupied by its own group of species, and these

groups not being mixed or interfused among each other to any great

extent. And thus, as the earth is occupied by various nations of

men, each appearing at first sight to be of a different stock, so

each other tribe of living things is scattered over the ground in a

similar manner, and distributed into its separate _nations_ in

distant countries. The places where species are thus peculiarly

found, are, in the case of plants, called their _stations_. Yet each

species in its own region loves and selects some peculiar conditions

of shade or exposure, soil or moisture: its place, defined by the

general description of such conditions, is called its _habitation_.

[Note 78\18: Lyell, _Principles_, B. iii. c. v.]

Not only each species thus placed in its own province, has its

position further fixed by its own habits, but more general groups

and assemblages are found to be determined in their situation by

more general conditions. Thus it is the character of the _flora_ of

a collection of islands, scattered through a wide ocean in a

tropical and humid climate, to contain an immense preponderance of

tree-ferns. In the same way, the situation and depth at which

certain genera of shells are found have been tabulated[79\18] by Mr.

Broderip. Such general inferences, if {563} they can be securely

made, are of extreme interest in their bearing on geological

speculations.

[Note 79\18: Greenough, _Add._ 1835, p. 20.]

The means by which plants and animals are now diffused from one

place to another, have been well described by Mr. Lyell.[80\18] And

he has considered also, with due attention, the manner in which they

become imbedded in mineral deposits of various kinds.[81\18] He has

thus followed the history of organized bodies, from the germ to the

tomb, and thence to the cabinet of the geologist.

[Note 80\18: Lyell, B. iii. c. v. vi. vii.]

[Note 81\18: B. iii. c. xiii. xiv. xv. xvi.]

But, besides the fortunes of individual plants and animals, there is

another class of questions, of great interest, but of great

difficulty;--the fortunes of each species. In what manner do species

which were not, begin to be? as geology teaches us that they many

times have done; and, as even our own reasonings convince us they must

have done, at least in the case of the species among which we live.

We here obviously place before us, as a subject of research, the

Creation of Living Things;--a subject shrouded in mystery, and not

to be approached without reverence. But though we may conceive,

that, on this subject, we are not to seek our belief from science

alone, we shall find, it is asserted, within the limits of allowable

and unavoidable speculation, many curious and important problems

which may well employ our physiological skill. For example, we may

ask:--how we are to recognize the species which were originally

created distinct?--whether the population of the earth at one

geological epoch could pass to the form which it has at a succeeding

period, by the agency of natural causes alone?--and if not, what

other account we can give of the succession which we find to have

taken place?

The most remarkable point in the attempts to answer these and the

like questions, is the controversy between the advocates and the

opponents of the doctrine of the _transmutation of species_. This

question is, even from its mere physiological import, one of great

interest; and the interest is much enhanced by our geological

researches, which again bring the question before us in a striking

form, and on a gigantic scale. We shall, therefore, briefly state

the point at issue.

_Sect._ 3.--_Question of the Transmutation of Species._

WE see that animals and plants may, by the influence of breeding,

and of external agents operating upon their constitution, be greatly

{564} modified, so as to give rise to varieties and races different

from what before existed. How different, for instance, is one kind

and breed of dog from another! The question, then, is, whether

organized beings can, by the mere working of natural causes, pass

from the type of one species to that of another? whether the wolf

may, by domestication, become the dog? whether the ourang-outang

may, by the power of external circumstances, be brought within the

circle of the human species? And the dilemma in which we are placed

is this;--that if species are not thus interchangeable, we must

suppose the fluctuations of which each species is capable, and which

are apparently indefinite, to be bounded by rigorous limits;

whereas, if we allow such a _transmutation of species_, we abandon

that belief in the adaptation of the structure of every creature to

its destined mode of being, which not only most persons would give

up with repugnance, but which, as we have seen, has constantly and

irresistibly impressed itself on the minds of the best naturalists,

as the true view of the order of the world.

But the study of Geology opens to us the spectacle of many groups of

species which have, in the course of the earth's history, succeeded

each other at vast intervals of time; one set of animals and plants

disappearing, as it would seem, from the face of our planet, and

others, which did not before exist, becoming the only occupants of

the globe. And the dilemma then presents itself to us anew:--either

we must accept the doctrine of the transmutation of species, and

must suppose that the organized species of one geological epoch were

transmuted into those of another by some long-continued agency of

natural causes; or else, we must believe in many successive acts of

creation and extinction of species, out of the common course of

nature; acts which, therefore, we may properly call miraculous.

This latter dilemma, however, is a question concerning the facts

which have happened in the history of the world; the deliberation

respecting it belongs to physical geology itself, and not to that

subsidiary science which we are now describing, and which is

concerned only with such causes as we know to be in constant and

orderly action.

The former question, of the limited or unlimited extent of the

modifications of animals and plants, has received full and careful

consideration from eminent physiologists; and in their opinions we

find, I think, an indisputable preponderance to that decision which

rejects the transmutation of species, and which accepts the former

side of the dilemma; namely, that the changes of which each species

is {565} susceptible, though difficult to define in words, are

limited in fact. It is extremely interesting and satisfactory thus

to receive an answer in which we can confide, to inquiries seemingly

so wide and bold as those which this subject involves. I refer to

Mr. Lyell, Dr. Prichard, Mr. Lawrence, and others, for the history

of the discussion, and for the grounds of the decision; and I shall

quote very briefly the main points and conclusions to which the

inquiry has led.[82\18]

[Note 82\18: Lyell, B. iii. c. iv.]

It may be considered, then, as determined by the over-balance of

physiological authority, that there is a capacity in all species to

accommodate themselves, to a certain extent, to a change of external

circumstances; this extent varying greatly according to the species.

There may thus arise changes of appearance or structure, and some of

these changes are transmissible to the offspring: but the mutations

thus superinduced are governed by constant laws, and confined within

certain limits. Indefinite divergence from the original type is not

possible; and the extreme limit of possible variation may usually be

reached in a brief period of time: in short, _species have a real

existence in nature_, and a transmutation from one to another does

not exist.

Thus, for example, Cuvier remarks, that notwithstanding all the

differences of size, appearance, and habits, which we find in the dogs

of various races and countries, and though we have (in the Egyptian

mummies) skeletons of this animal as it existed three thousand years

ago, the relation of the bones to each other remains essentially the

same; and, with all the varieties of their shape[83\18] and size,

there are characters which resist all the influences both of external

nature, of human intercourse, and of time.

[Note 83\18: _Ossem. Foss._ Disc. Prél. p. 61.]

_Sect._ 4.--_Hypothesis of Progressive Tendencies._

WITHIN certain limits, however, as we have said, external

circumstances produce changes in the forms of organized beings. The

causes of change, and the laws and limits of their effects, as they

obtain in the existing state of the organic creation, are in the

highest degree interesting. And, as has been already intimated, the

knowledge thus obtained, has been applied with a view to explain the

origin of the existing population of the world, and the succession

of its past conditions. But those who have attempted such an

explanation, have found it necessary to assume certain additional

laws, in order to enable themselves to {566} deduce, from the tenet

of the transmutability of the species of organized beings, such a

state of things as we see about us, and such a succession of states

as is evidenced by geological researches. And here, again, we are

brought to questions of which we must seek the answers from the most

profound physiologists. Now referring, as before, to those which

appear to be the best authorities, it is found that these additional

positive laws are still more inadmissible than the primary

assumption of indefinite capacity of change. For example, in order

to account, on this hypothesis, for the seeming adaptation of the

endowments of animals to their wants, it is held that the endowments

are the result of the wants; that the swiftness of the antelope, the

claws and teeth of the lion, the trunk of the elephant, the long

neck of the giraffe have been produced by a certain plastic

character in the constitution of animals, operated upon, for a long

course of ages, by the attempts which these animals made to attain

objects which their previous organization did not place within their

reach. In this way, it is maintained that the most striking

attributes of animals, those which apparently imply most clearly the

providing skill of their Creator, have been brought forth by the

long-repeated efforts of the creatures to attain the object of their

desire; thus animals with the highest endowments have been gradually

developed from ancestral forms of the most limited organization;

thus fish, bird, and beast, have grown from _small gelatinous

bodies_, "petits corps gelatineux," possessing some obscure

principle of life, and the capacity of development; and thus man

himself with all his intellectual and moral, as well as physical

privileges, has been derived from some creature of the ape or baboon

tribe, urged by a constant tendency to improve, or at least to alter

his condition.

As we have said, in order to arrive even hypothetically at this

result, it is necessary to assume besides a mere capacity for

change, other positive and active principles, some of which we may

notice. Thus, we must have as the direct productions of nature on

this hypothesis, certain monads or rough draughts, the primary

_rudiments_ of plants and animals. We must have, in these, a

constant _tendency to progressive improvement_, to the attainment of

higher powers and faculties than they possess; which tendency is

again perpetually modified and controlled by the _force of external

circumstances_. And in order to account for the simultaneous

existence of animals in every stage of this imaginary progress, we

must suppose that nature is compelled to be _constantly_ producing

those elementary beings, from which all animals are successively

developed. {567}

I need not stay to point out how extremely arbitrary every part of

this scheme is; and how complex its machinery would be, even if it

did account for the facts. It may be sufficient to observe, as

others have done,[84\18] that the capacity of change, and of being

influenced by external circumstances, such as we really find it in

nature, and therefore such as in science we must represent it, is a

tendency, not to improve, but to deteriorate. When species are

modified by external causes, they usually degenerate, and do not

advance. And there is no instance of a species acquiring an entirely

new sense, faculty, or organ, in addition to, or in the place of,

what it had before.

[Note 84\18: Lyell, B. III. c. iv.]

Not only, then, is the doctrine of the transmutation of species in

itself disproved by the best physiological reasonings, but the

additional assumptions which are requisite, to enable its advocates

to apply it to the explanation of the geological and other phenomena

of the earth, are altogether gratuitous and fantastical.

Such is the judgment to which we are led by the examination of the

discussions which have taken place on this subject. Yet in certain

speculations, occasioned by the discovery of the _Sivatherium_, a

new fossil animal from the Sub-Himalaya mountains of India, M.

Geoffroy Saint-Hilaire speaks of the belief in the immutability of

species as a conviction which is fading away from men's minds. He

speaks too of the termination of the age of Cuvier, "la clôture du

siècle de Cuvier," and of the commencement of a better zoological

philosophy.[85\18] But though he expresses himself with great

animation, I do not perceive that he adduces, in support of his

peculiar opinions, any arguments in addition to those which he urged

during the lifetime of Cuvier. And the reader[86\18] may recollect

that the consideration of that controversy led us to very different

anticipations from his, respecting the probable future progress of

physiology. The discovery of the Sivatherium supplies no particle of

proof to the hypothesis, that the existing species of animals are

descended from extinct creatures which are specifically distinct:

and we cannot act more wisely than in listening to the advice of

that eminent naturalist, M. de Blainville.[87\18] "Against this

hypothesis, which, up to the present time, I regard as purely

gratuitous, and likely to turn geologists out of the sound and

excellent road in which they now are, I willingly raise my voice,

with the most absolute conviction of being in the right." {568}

[Note 85\18: _Compte Rendu de l'Acad. des Sc._ 1837, No. 3, p. 81.]

[Note 86\18: See B. XVII. c. vii.]

[Note 87\18: _Compte Rendu_, 1837, No. 5, p. 168.]

[2nd Ed.] [The hypothesis of the progressive developement of species

has been urged recently, in connexion with the physiological tenet

of Tiedemann and De Serres, noticed in B. XVII. c. vii. sect.

3;--namely, that the embryo of the higher forms of animals passes by

gradations through those forms which are permanent in inferior

animals. Assuming this tenet as exact, it has been maintained that

the higher animals which are found in the more recent strata may

have been produced by an ulterior development of the lower forms in

the embryo state; the circumstances being such as to favor such a

developement. But all the best physiologists agree in declaring that

such an extraordinary developement of the embryo is inconsistent

with physiological possibility. Even if the progression of the

embryo in time have a general correspondence with the order of

animal forms as more or less perfectly organized (which is true in

an extremely incomplete and inexact degree), this correspondence

must be considered, not as any indication of causality, but as one

of those marks of universal analogy and symmetry which are stamped

upon every part of the creation.

Mr. Lyell[88\18] notices this doctrine of Tiedemann and De Serres;

and observes, that though nature presents us with cases of animal

forms degraded by incomplete developement, she offers none of forms

exalted by extraordinary developement. Mr. Lyell's own hypothesis of

the introduction of new species upon the earth, not having any

physiological basis, hardly belongs to this chapter.]

[Note 88\18: _Principles_, B. III. c. iv.]

_Sect._ 5.--_Question of Creation as related to Science._

BUT since we reject the production of new species by means of

external influence, do we then, it may be asked, accept the other

side of the dilemma which we have stated; and admit a series of

creations of species, by some power beyond that which we trace in

the ordinary course of nature?

To this question, the history and analogy of science, I conceive,

teach us to reply as follows:--All palætiological sciences, all

speculations which attempt to ascend from the present to the remote

past, by the chain of causation, do also, by an inevitable

consequence, urge us to look for the beginning of the state of

things which we thus contemplate; but in none of these cases have

men been able, by the aid of science, to arrive at a beginning which

is homogeneous with the {569} known course of events. The first

origin of language, of civilization, of law and government, cannot

be clearly made out by reasoning and research; just as little, we

may expect, will a knowledge of the origin of the existing and

extinct species of plants and animals, be the result of

physiological and geological investigation.

But, though philosophers have never yet demonstrated, and perhaps

never will be able to demonstrate, what was that primitive state of

things in the social and material worlds, from which the progressive

state took its first departure; they can still, in all the lines of

research to which we have referred, go very far back;--determine many

of the remote circumstances of the past sequence of events;--ascend to

a point which, from our position at least, seems to be near the

origin;--and exclude many suppositions respecting the origin itself.

Whether, by the light of reason alone, men will ever be able to do

more than this, it is difficult to say. It is, I think, no irrational

opinion, even on grounds of philosophical analogy alone, that in all

those sciences which look back and seek a beginning of things, we may

be unable to arrive at a consistent and definite belief, without

having recourse to other grounds of truth, as well as to historical

research and scientific reasoning. When our thoughts would apprehend

steadily the creation of things, we find that we are obliged to summon

up other ideas than those which regulate the pursuit of scientific

truths;--to call in other powers than those to which we refer natural

events: it cannot, then, be considered as very surprizing, if, in this

part of our inquiry, we are compelled to look for other than the

ordinary evidence of science.

Geology, forming one of the palætiological class of sciences, which

trace back the history of the earth and its inhabitants on

philosophical grounds, is thus associated with a number of other

kinds of research, which are concerned about language, law, art, and

consequently about the internal faculties of man, his thoughts, his

social habits, his conception of right, his love of beauty. Geology

being thus brought into the atmosphere of moral and mental

speculations, it may be expected that her investigations of the

probable past will share an influence common to them; and that she

will not be allowed to point to an origin of her own, a merely

physical beginning of things; but that, as she approaches towards

such a goal, she will be led to see that it is the origin of many

trains of events, the point of convergence of many lines. It may be,

that instead of being allowed to travel up to this focus of being,

we are only able to estimate its place and nature, and {570} to form

of it such a judgment as this;--that it is not only the source of

mere vegetable and animal life, but also of rational and social

life, language and arts, law and order; in short, of all the

progressive tendencies by which the highest principles of the

intellectual and moral world have been and are developed, as well as

of the succession of organic forms, which we find scattered, dead or

living, over the earth.

This reflection concerning the natural scientific view of creation,

it will be observed, has not been sought for, from a wish to arrive

at such conclusions; but it has flowed spontaneously from the manner

in which we have had to introduce geology into our classification of

the sciences; and this classification was framed from an unbiassed

consideration of the general analogies and guiding ideas of the

various portions of our knowledge. Such remarks as we have made may

on this account be considered more worthy of attention.

But such a train of thought must be pursued with caution. Although

it may not be possible to arrive at a right conviction respecting

the origin of the world, without having recourse to other than

physical considerations, and to other than geological evidence: yet

extraneous considerations, and extraneous evidence, respecting the

nature of the beginning of things, must never be allowed to

influence our physics or our geology. Our geological dynamics, like

our astronomical dynamics, may be inadequate to carry us back to an

origin of that state of things, of which it explains the progress:

but this deficiency must be supplied, not by adding supernatural to

natural geological dynamics, but by accepting, in their proper

place, the views supplied by a portion of knowledge of a different

character and order. If we include in our Theology the speculations

to which we have recourse for this purpose, we must exclude from

them our Geology. The two sciences may conspire, not by having any

part in common: but because, though widely diverse in their lines,

both point to a mysterious and invisible origin of the world.

All that which claims our assent on those higher grounds of which

theology takes cognizance, must claim such assent as is consistent

with those grounds; that is, it must require belief in respect of

all that bears upon the highest relations of our being, those on

which depend our duties and our hopes. Doctrines of this kind may

and must be conveyed and maintained, by means of information

concerning the past history of man, and his social and material, as

well as moral and spiritual fortunes. He who believes that a

Providence has {571} ruled the affairs of mankind, will also believe

that a Providence has governed the material world. But any language

in which the narrative of this government of the material world can

be conveyed, must necessarily be very imperfect and inappropriate;

being expressed in terms of those ideas which have been selected by

men, in order to describe appearances and relations of created

things as they affect one another. In all cases, therefore, where we

have to attempt to interpret such a narrative, we must feel that we

are extremely liable to err; and most of all, when our

interpretation refers to those material objects and operations which

are most foreign to the main purpose of a history of providence. If

we have to consider a communication containing a view of such a

government of the world, imparted to us, as we may suppose, in order

to point out the right direction for our feelings of trust, and

reverence, and hope, towards the Governor of the world, we may

expect that we shall be in no danger of collecting from our

authority erroneous notions with regard to the power, and wisdom,

and goodness of His government; or with respect to our own place,

duties, and prospects, and the history of our race so far as our

duties and prospects are concerned. But that we shall rightly

understand the detail of all events in the history of man, or of the

skies, or of the earth, which are narrated for the purpose of thus

giving a right direction to our minds, is by no means equally

certain; and I do not think it would be too much to say, that an

immunity from perplexity and error, in such matters, is, on general

grounds, very improbable. It cannot then surprise us to find, that

parts of such narrations which seem to refer to occurrences like

those of which astronomers and geologists have attempted to

determine the laws, have given rise to many interpretations, all

inconsistent with one another, and most of them at variance with the

best established principles of astronomy and geology.

It may be urged, that all truths must be consistent with all other

truths, and that therefore the results of true geology or astronomy

cannot be irreconcileable with the statements of true theology. And

this universal consistency of truth with itself must be assented to;

but it by no means follows that we must be able to obtain a full

insight into the nature and manner of such a consistency. Such an

insight would only be possible if we could obtain a clear view of

that central body of truth, the source of the principles which

appear in the separate lines of speculation. To expect that we

should see clearly how the providential government of the world is

consistent with the unvarying laws {572} by which its motions and

developements are regulated, is to expect to understand thoroughly

the laws of motion, of developement, and of providence; it is to

expect that we may ascend from geology and astronomy to the creative

and legislative centre, from which proceeded earth and stars; and

then descend again into the moral and spiritual world, because its

source and centre are the same as those of the material creation. It

is to say that reason, whether finite or infinite, must be

consistent with itself; and that, therefore, the finite must be able

to comprehend the infinite, to travel from any one province of the

moral and material universe to any other, to trace their bearing,

and to connect their boundaries.

One of the advantages of the study of the history and nature of

science in which we are now engaged is, that it warns us of the

hopeless and presumptuous character of such attempts to understand

the government of the world by the aid of science, without throwing

any discredit upon the reality of our knowledge;--that while it

shows how solid and certain each science is, so long as it refers

its own facts to its own ideas, it confines each science within its

own limits, and condemns it as empty and helpless, when it

pronounces upon those subjects which are extraneous to it. The error

of persons who should seek a geological narrative in theological

records, would be rather in the search itself than in their

interpretation of what they might find; and in like manner the error

of those who would conclude against a supernatural beginning, or a

providential direction of the world, upon geological or

physiological reasonings, would be, that they had expected those

sciences alone to place the origin or the government of the world in

its proper light.

Though these observations apply generally to all the palætiological

sciences, they may be permitted here, because they have an especial

bearing upon some of the difficulties which have embarrassed the

progress of geological speculation; and though such difficulties

are, I trust, nearly gone by, it is important for us to see them in

their true bearing.

From what has been said, it follows that geology and astronomy are,

of themselves, incapable of giving us any distinct and satisfactory

account of the origin of the universe, or of its parts. We need not

wonder, then, at any particular instance of this incapacity; as, for

example, that of which we have been speaking, the impossibility of

accounting by any natural means for the production of all the

successive tribes of plants and animals which have peopled the world

in the {573} various stages of its progress, as geology teaches us.

That they were, like our own animal and vegetable contemporaries,

profoundly adapted to the condition in which they were placed, we

have ample reason to believe; but when we inquire whence they came

into this our world, geology is silent. The mystery of creation is

not within the range of her legitimate territory; she says nothing,

but she points upwards.

_Sect._ 6.--_The Hypothesis of the regular Creation and Extinction

of Species._

1. _Creation of Species._--We have already seen, how untenable, as a

physiological doctrine, is the principle of the transmutability and

progressive tendency of species; and therefore, when we come to

apply to theoretical geology the principles of the present chapter,

this portion of the subject will easily be disposed of. I hardly

know whether I can state that there is any other principle which has

been applied to the solution of the geological problem, and which,

therefore, as a general truth, ought to be considered here. Mr.

Lyell, indeed, has spoken[89\18] of an hypothesis that "the

successive creation of species may constitute a regular part of the

economy of nature:" but he has nowhere, I think, so described this

process as to make it appear in what department of science we are to

place the hypothesis. Are these new species created by the

production, at long intervals, of an offspring different in species

from the parents? Or are the species so created produced without

parents? Are they gradually evolved from some embryo substance? or

do they suddenly start from the ground, as in the creation of the

poet?

. . . . . . . Perfect forms

Limbed and full-grown: out of the ground up rose

As from his lair, the wild beast where he wons

In forest wild, in thicket, brake, or den; . . .

The grassy clods now calved; now half appeared

The tawny lion, pawing to get free

His hinder parts; then springs as broke from bounds,

And rampant shakes his brinded mane; &c. &c.

_Paradise Lost_, B. vii.

[Note 89\18: B. III. c. xi. p. 234.]

Some selection of one of these forms of the hypothesis, rather than

the others, with evidence for the selection, is requisite to entitle

us to {574} place it among the known causes of change which in this

chapter we are considering. The bare conviction that a creation of

species has taken place, whether once or many times, so long as it

is unconnected with our organical sciences, is a tenet of Natural

Theology rather than of Physical Philosophy.

[2nd Ed.] [Mr. Lyell has explained his theory[90\18] by supposing

man to people a great desert, introducing into it living plants and

animals: and he has traced, in a very interesting manner, the

results of such a hypothesis on the distribution of vegetable and

animal species. But he supposes the agents who do this, before they

import species into particular localities, to study attentively the

climate and other physical conditions of each spot, and to use

various precautions. It is on account of the notion of design thus

introduced that I have, above, described this opinion as rather a

tenet of Natural Theology than of Physical Philosophy.

[Note 90\18: B. III. c. viii. p. 166.]

Mr. Edward Forbes has published some highly interesting speculations

on the distribution of existing species of animals and plants. It

appears that the manner in which animal and vegetable forms are now

diffused requires us to assume centres from which the diffusion took

place by no means limited by the present divisions of continents and

islands. The changes of land and water which have thus occurred

since the existing species were placed on the earth must have been

very extensive, and perhaps reach into the glacial period of which I

have spoken above.[91\18]

[Note 91\18: See, in _Memoirs of the Geological Survey of Great

Britain_, vol. i. p. 336, Professor Forbes's Memoir "On the

Connection between the Distribution of the existing Fauna and Flora

of the British Isles, and the Geological Changes which have affected

their area, especially during the epoch of the Northern Drift."]

According to Mr. Forbes's views, for which he has offered a great

body of very striking and converging reasons, the present vegetable

and animal population of the British Isles is to be accounted for by

the following series of events. The marine deposits of the

_meiocine_ formation were elevated into a great Atlantic continent,

yet separate from what is now America, and having its western shore

where now the great semi-circular belt of gulf-weed ranges from the

15th to the 45th parallel of latitude. This continent then became

stocked with life, and of its vegetable population, the flora of the

west of Ireland, which has many points in common with the flora of

Spain and the {575} Atlantic islands (the _Asturian_ flora), is the

record. The region between Spain and Ireland, and the rest of this

meiocene continent, was destroyed by some geological movement, but

there were left traces of the connexion which still remain.

Eastwards of the flora just mentioned, there is a flora common to

Devon and Cornwall, to the south-east part of Ireland, the Channel

Isles, and the adjacent provinces of France;--a flora passing to a

southern character; and having its course marked by the remains of a

great rocky barrier, the destruction of which probably took place

anterior to the formation of the narrower part of the channel.

Eastward from this _Devon_ or _Norman_ flora, again, we have the

_Kentish_ flora, which is an extension of the flora of North-western

France, insulated by the breach which formed the straits of Dover.

Then came the _Glacial period_, when the east of England and the

north of Europe were submerged, the northern drift was distributed,

and England was reduced to a chain of islands or ridges, formed by

the mountains of Wales, Cumberland, and Scotland, which were

connected with the land of Scandinavia. This was the period of

glaciers, of the dispersion of boulders, of the grooving and

scratching of rocks as they are now found. The climate being then

much colder than it now is, the flora, even down to the water's

edge, consisted of what are now Alpine plants; and this _Alpine_

flora is common to Scandinavia and to our mountain-summits. And

these plants kept their places, when, by the elevation of the land,

the whole of the present German Ocean became a continent connecting

Britain with central Europe. For the increased elevation of their

stations counterbalanced the diminished cold of the succeeding

period. Along the dry bed of the German Sea, thus elevated, the

principal part of the existing flora of England, the _Germanic_

flora, migrated. A large portion of our existing animal population

also came over through the same region; and along with those, came

hyenas, tigers, rhinoceros, aurochs, elk, wolves, beavers, which are

extinct in Britain, and other animals which are extinct altogether,

as the primigenian elephant or mammoth. But then, again, the German

Ocean and the Irish Channel were scooped out; and the climate again

changed. In our islands, so detached, many of the larger beasts

perished, and their bones were covered up in peat-mosses and caves,

where we find them. This distinguished naturalist has further shown

that the population of the sea lends itself to the same view. Mr.

Forbes says that the writings of Mr. Smith, of Jordan-hill, "On the

last Changes in the relative Levels of the Land and Sea in the

British Islands," published in the _Memoirs of the_ {576} _Wernerian

Society for_ 1837-8, must be esteemed the foundation of a critical

investigation of this subject in Britain.]

2. _Extinction of Species._--With regard to the extinction of

species Mr. Lyell has propounded a doctrine which is deserving of

great attention here. Brocchi, when he had satisfied himself, by

examination of the Sub-Apennines, that about half the species which

had lived at the period of their deposition, had since become

extinct, suggested as a possible cause for this occurrence, that the

vital energies of a species, like that of an individual, might

gradually decay in the progress of time and of generations, till at

last the prolific power might fail, and the species wither away.

Such a property would be conceivable as a physiological fact; for we

see something of the kind in fruit-trees propagated by cuttings:

after some time, the stock appears to wear out, and loses its

peculiar qualities. But we have no sufficient evidence that this is

the case in generations of creatures continued by the reproductive

powers. Mr. Lyell conceives, that, without admitting any inherent

constitutional tendency to deteriorate, the misfortunes to which

plants and animals are exposed by the change of the physical

circumstances of the earth, by the alteration of land and water, and

by the changes of climate, must very frequently occasion the loss of

several species. We have historical evidence of the extinction of

one conspicuous species, the Dodo, a bird of large size and singular

form, which inhabited the Isle of France when that island was first

discovered, and which now no longer exists. Several other species of

animals and plants seem to be in the course of vanishing from the

face of the earth, even under our own observation. And taking into

account the greater changes of the surface of the globe which

geology compels us to assume, we may imagine many or all the

existing species of living things to be extirpated. If, for

instance, that reduction of the climate of the earth which appears,

from geological evidence, to have taken place already, be supposed

to go on much further, the advancing snow and cold of the polar

regions may destroy the greater part of our plants and animals, and

drive the remainder, or those of them which possess the requisite

faculties of migration and accommodation, to seek an asylum near the

equator. And if we suppose the temperature of the earth to be still

further reduced, this zone of now-existing life, having no further

place of refuge, will perish, and the whole earth will be tenanted,

if at all, by a new creation. Other causes might produce the same

effect as a change of climate; and, without supposing such causes to

affect the whole globe, it is easy to {577} imagine circumstances

such as might entirely disturb the equilibrium which the powers of

diffusion of different species have produced;--might give to some

the opportunity of invading and conquering the domain of others; and

in the end, the means of entirely suppressing them, and establishing

themselves in their place.

That this extirpation of certain species, which, as we have seen,

happens in a few cases under common circumstances, might happen upon

a greater scale, if the range of external changes were to be much

enlarged, cannot be doubted. The extent, therefore, to which natural

causes may account for the extinction of species, will depend upon

the amount of change which we suppose in the physical conditions of

the earth. It must be a task of extreme difficulty to estimate the

effect upon the organic world, even if the physical circumstances

were given. To determine the physical condition to which a given

state of the earth would give rise, I have already noted as another

very difficult problem. Yet these two problems must be solved, in

order to enable us to judge of the sufficiency of any hypothesis of

the extinction of species; and in the mean time, for the mode in

which new species come into the places of those which are

extinguished, we have (as we have seen) no hypothesis which

physiology can, for a moment, sanction.

_Sect._ 7.--_The Imbedding of Organic Remains._

THERE is still one portion of the Dynamics of Geology, a branch of

great and manifest importance, which I have to notice, but upon

which I need only speak very briefly. The mode in which the spoils

of existing plants and animals are imbedded in the deposits now

forming, is a subject which has naturally attracted the attention of

geologists. During the controversy which took place in Italy

respecting the fossils of the Sub-Apennine hills, Vitaliano

Donati,[92\18] in 1750, undertook an examination of the Adriatic,

and found that deposits containing shells and corals, extremely

resembling the strata of the hills, were there in the act of

formation. But without dwelling on other observations of like kind,

I may state that Mr. Lyell has treated this subject, and all the

topics connected with it, in a very full and satisfactory manner. He

has explained,[93\18] by an excellent collection of illustrative

facts, how deposits of various substance and contents are formed;

how plants and animals become fossil in peat, in blown sand, in

volcanic matter, in {578} alluvial soil, in caves, and in the beds

of lakes and seas. This exposition is of the most instructive

character, as a means of obtaining right conclusions concerning the

causes of geological phenomena. Indeed, in many cases, the

similarity of past effects with operations now going on, is so

complete, that they may be considered as identical; and the

discussion of such cases belongs, at the same time, to Geological

Dynamics and to Physical Geology; just as the problem of the fall of

meteorolites may be considered as belonging alike to mechanics and

to physical astronomy. The growth of modern peat-mosses, for

example, fully explains the formation of the most ancient: objects

are buried in the same manner in the ejections of active and of

extinct volcanoes; within the limits of history, many estuaries have

been filled up; and in the deposits which have occupied these

places, are strata containing shells,[94\18] as in the older

formations.

[Note 92\18: Lyell, B. I. c. iii. p. 67. (4th ed.)]

[Note 93\18: B. III. c. xiii. xiv. xv. xvi. xvii.]

[Note 94\18: Lyell, B. III. c. xvii. p. 286. See also his Address to

the Geological Society in 1837, for an account of the Researches of

Mr. Stokes and of Professor Göppert, on the lapidification of

vegetables.]

{{579}}

PHYSICAL GEOLOGY.

CHAPTER VII.

PROGRESS OF PHYSICAL GEOLOGY.

_Sect._ 1.--_Object and Distinctions of Physical Geology._

BEING, in consequence of the steps which we have attempted to

describe, in possession of two sciences, one of which traces the

laws of action of known causes, and the other describes the

phenomena which the earth's surface presents, we are now prepared to

examine how far the attempts to refer the facts to their causes have

been successful: we are ready to enter upon the consideration of

Theoretical or _Physical_ Geology, as, by analogy with Physical

Astronomy, we may term this branch of speculation.

The distinction of this from other portions of our knowledge is

sufficiently evident. In former times, Geology was always associated

with Mineralogy, and sometimes confounded with it; but the mistake

of such an arrangement must be clear, from what has been said.

Geology is connected with Mineralogy, only so far as the latter

science classifies a large portion of the objects which Geology

employs as evidence of its statements. To confound the two is the

same error as it would be to treat philosophical history as

identical with the knowledge of medals. Geology procures evidence of

her conclusions wherever she can; from minerals or from seas; from

inorganic or from organic bodies; from the ground or from the skies.

The geologist's business is to learn the past history of the earth;

and he is no more limited to one or a few kinds of documents, as his

sources of information, than is the historian of man, in the

execution of a similar task.

Physical Geology, of which I now speak, may not be always easily

separable from Descriptive Geology: in fact, they have generally

been combined, for few have been content to describe, without

attempting in some measure to explain. Indeed, if they had done so,

it is {580} probable that their labors would have been far less

zealous, and their expositions far less impressive. We by no means

regret, therefore, the mixture of these two kinds of knowledge,

which has so often occurred; but still, it is our business to

separate them. The works of astronomers before the rise of sound

physical astronomy, were full of theories, but these were

advantageous, not prejudicial, to the progress of the science.

Geological theories have been abundant and various; but yet our

history of them must be brief. For our object is, as must be borne in

mind, to exhibit these, only so far as they are steps discoverably

tending to the _true_ theory of the earth: and in most of them we do

not trace this character. Or rather, the portions of the labors of

geologists which do merit this praise, belong to the two preceding

divisions of the subject, and have been treated of there.

The history of Physical Geology, considered as the advance towards a

science as real and stable as those which we have already treated of

(and this is the form in which we ought to trace it), hitherto

consists of few steps. We hardly know whether the progress is begun.

The history of Physical Astronomy almost commences with Newton, and

few persons will venture to assert that the Newton of Geology has

yet appeared.

Still, some examination of the attempts which have been made is

requisite, in order to explain and justify the view which the

analogy of scientific history leads us to take, of the state of the

subject. Though far from intending to give even a sketch of all past

geological speculations, I must notice some of the forms such

speculations have at different times assumed.

_Sect._ 2.--_Of Fanciful Geological Opinions._

REAL and permanent geological knowledge, like all other physical

knowledge, can be obtained only by inductions of classification and

law from many clearly seen phenomena. The labor of the most active,

the talent of the most intelligent, are requisite for such a

purpose. But far less than this is sufficient to put in busy

operation the inventive and capricious fancy. A few appearances

hastily seen, and arbitrarily interpreted, are enough to give rise

to a wondrous tale of the past, full of strange events and

supernatural agencies. The mythology and early poetry of nations

afford sufficient evidence of man's love of the wonderful, and of

his inventive powers, in early stages of intellectual development.

The scientific faculty, on the other hand, {581} and especially that

part of it which is requisite for the induction of laws from facts,

emerges slowly and with difficulty from the crowd of adverse

influences, even under the most favorable circumstances. We have

seen that in the ancient world, the Greeks alone showed themselves

to possess this talent; and what they thus attained to, amounted

only to a few sound doctrines in astronomy, and one or two extremely

imperfect truths in mechanics, optics, and music, which their

successors were unable to retain. No other nation, till we come to

the dawn of a better day in modern Europe, made any positive step at

all in sound physical speculation. Empty dreams or useless

exhibitions of ingenuity, formed the whole of their essays at such

knowledge.

It must, therefore, independently of positive evidence, be

considered as extremely improbable, that any of these nations

should, at an early period, have arrived, by observation and

induction, at wide general truths, such as the philosophers of

modern times have only satisfied themselves of by long and patient

labor and thought. If resemblances should be discovered between the

assertions of ancient writers and the discoveries of modern science,

the probability in all cases, the certainty in most, is that these

are accidental coincidences;--that the ancient opinion is no

anticipation of the modern discovery, but is one guess among many,

not a whit the more valuable because its expression agrees with a

truth. The author of the guess could not intend the truth, because

his mind was not prepared to comprehend it. Those of the ancients

who spoke of the _harmony_ which binds all things together, could

not mean the Newtonian gravitation, because they had never been led

to conceive an attractive force, governed by definite mathematical

laws in its quantity and operation.

In agreement with these views, we must, I conceive, estimate the

opinions which we find among the ancients, respecting the changes

which the earth's surface has undergone. These opinions, when they

are at all of a general kind, are arbitrary fictions of the fancy,

showing man's love of generality indeed, but indulging it without

that expense of labor and thought which alone can render it

legitimate.

We might, therefore, pass by all the traditions and speculations of

Oriental, Egyptian, and Greek cosmogony, as extraneous to our

subject. But since these have recently been spoken of, as

conclusions collected, however vaguely, from observed facts,[95\18]

we may make a remark or two upon them. {582}

[Note 95\18: Lyell, B. i. c. ii. p. 8. (4th ed.)]

The notion of a series of creations and destructions of worlds,

which appears in the sacred volume of the Hindoos, which formed part

of the traditionary lore of Egypt, and which was afterwards adopted

into the poetry and philosophy of Greece, must be considered as a

mythological, not a physical, doctrine. When this doctrine was dwelt

upon, men's thoughts were directed, not to the terrestrial facts

which it seemed to explain, but to the attributes of the deities

which it illustrated. The conception of a Supreme power, impelling

and guiding the progress of events, which is permanent among all

perpetual change, and regular among all seeming chance, was readily

entertained by contemplative and enthusiastic minds; and when

natural phenomena were referred to this doctrine, it was rather for

the purpose of fastening its impressiveness upon the senses, than in

the way of giving to it authority and support. Hence we perceive

that in the exposition of this doctrine, an attempt was always made

to fill and elevate the mind with the notions of marvellous events,

and of infinite times, in which vast cycles of order recurred. The

"great year," in which all celestial phenomena come round, offered

itself as capable of being calculated; and a similar great year was

readily assumed for terrestrial and human events. Hence there were

to be brought round by great cycles, not only deluges and

conflagrations which were to destroy and renovate the earth, but

also the series of historical occurrences. Not only the sea and land

were to recommence their alternations, but there was to be another

Argo, which should carry warriors on the first sea-foray,[96\18] and

another succession of heroic wars. Looking at the passages of

ancient authors which refer to terrestrial changes in this view, we

shall see that they are addressed almost entirely to the love of the

marvellous and the infinite, and cannot with propriety be taken as

indications of a spirit of physical philosophy. For example, if we

turn to the celebrated passage in Ovid,[97\18] where Pythagoras is

represented as asserting that land becomes sea, and sea land, and

many other changes which geologists have verified, we find that

these observations are associated with many fables, as being matter

of exactly the same kind;--the fountain of Ammon which was cold by

day and warm by night;[98\18]--the waters of Salmacis which

effeminate men;--the Clitorian spring which makes them loathe

wine;--the Simplegades islands which were once moveable;--the

Tritonian lake which covered men's bodies with feathers;--and many

similar marvels. And the general purport of {583} the whole is, to

countenance the doctrine of the metempsychosis, and the Pythagorean

injunction of not eating animal food. It is clear, I think, that

facts so introduced must be considered as having been contemplated

rather in the spirit of poetry than of science.

[Note 96\18: Virg. _Eclog._ 4.]

[Note 97\18: _Met._ Lib. xv.]

[Note 98\18: V. 309, &c.]

We must estimate in the same manner, the very remarkable passage

brought to light by M. Elie de Beaumont,[99\18] from the Arabian

writer, Kazwiri; in which we have a representation of the same spot

of ground, as being, at successive intervals of five hundred years,

a city, a sea, a desert, and again a city. This invention is

adduced, I conceive, rather to feed the appetite of wonder, than to

fix it upon any reality: as the title of his book, _The Marvels of

Nature_ obviously intimates.

[Note 99\18: _Ann. des Sc. Nat._ xxv. 380.]

The speculations of Aristotle, concerning the exchanges of land and

sea which take place in long periods, are not formed in exactly the

same spirit, but they are hardly more substantial; and seem to be

quite as arbitrary, since they are not confirmed by any examples and

proofs. After stating,[100\18] that the same spots of the earth are

not always land and always water, he gives the reason. "The

principle and cause of this is," he says, "that the inner parts of

the earth, like the bodies of plants and animals, have their ages of

vigor and of decline; but in plants and animals all the parts are in

vigor, and all grow old, at once: in the earth different parts

arrive at maturity at different times by the operation of cold and

heat: they grow and decay on account of the sun and the revolution

of the stars, and thus the parts of the earth acquire different

power, so that for a certain time they remain moist, and then become

dry and old: and then other places are revivified, and become

partially watery." We are, I conceive, doing no injustice to such

speculations by classing them among _fanciful_ geological opinions.

[Note 100\18: _Meteorol._ i. 14.]

We must also, I conceive, range in the same division another class

of writers of much more modern times;--I mean those who have trained

their geology by interpretations of Scripture. I have already

endeavored to show that such an attempt is a perversion of the

purpose of a divine communication, and cannot lead to any physical

truth. I do not here speak of geological speculations in which the

Mosaic account of the deluge has been referred to; for whatever

errors may have been committed on that subject, it would be as

absurd to disregard the most ancient historical record, in

attempting to trace back the history of the earth, as it would be,

gratuitously to reject any other {584} source of information. But

the interpretations of the account of the creation have gone further

beyond the limits of sound philosophy: and when we look at the

arbitrary and fantastical inventions by which a few phrases of the

writings of Moses have been moulded into complete systems, we cannot

doubt that these interpretations belong to the present Section.

I shall not attempt to criticize, nor even to enumerate, these

Scriptural Geologies,--_Sacred Theories of the Earth_, as Burnet

termed his. Ray, Woodward, Whiston, and many other persons to whom

science has considerable obligations, were involved, by the

speculative habits of their times, in these essays; and they have

been resumed by persons of considerable talent and some knowledge,

on various occasions up to the present day; but the more geology has

been studied on its own proper evidence, the more have geologists

seen the unprofitable character of such labors.

I proceed now to the next step in the progress of Theoretical

Geology.

_Sect._ 3.--_Of Premature Geological Theories._

WHILE we were giving our account of Descriptive Geology, the

attentive reader would perceive that we did, in fact, state several

steps in the advance towards general knowledge; but when, in those

cases, the theoretical aspect of such discoveries softened into an

appearance of mere classification, the occurrence was assigned to

the history of Descriptive rather than of Theoretical Geology. Of

such a kind was the establishment, by a long and vehement

controversy, of the fact, that the impressions in rocks are really

the traces of ancient living things; such, again, were the division

of rocks into Primitive, Secondary, Tertiary; the ascertainment of

the orderly succession of organic remains: the consequent fixation

of a standard series of formations and strata; the establishment of

the igneous nature of trap rocks; and the like. These are geological

truths which are assumed and implied in the very language which

geology uses; thus showing how in this, as in all other sciences,

the succeeding steps involve the preceding. But in the history of

geological theory, we have to consider the wider attempts to combine

the facts, and to assign them to their causes.

The close of the last century produced two antagonist theories of

this kind, which long maintained a fierce and doubtful

struggle;--that of Werner and that of Hutton: the one termed

_Neptunian_, from its {585} ascribing the phenomena of the earth's

surface mainly to aqueous agency; the other _Plutonian_ or

_Vulcanian_, because it employed the force of subterraneous fire as

its principal machinery. The circumstance which is most worthy of

notice in these remarkable essays is, the endeavor to give, by means

of such materials as the authors possessed, a complete and simple

account of all the facts of the earth's history. The Saxon

professor, proceeding on the examination of a small district in

Germany, maintained the existence of a chaotic fluid, from which a

series of universal formations had been precipitated, the position

of the strata being broken up by the falling in of subterraneous

cavities, in the intervals between these depositions. The Scotch

philosopher, who had observed in England and Scotland, thought

himself justified in declaring that the existing causes were

sufficient to spread new strata on the bottom of the ocean, and that

they are consolidated, elevated, and fractured by volcanic heat, so

as to give rise to new continents.

It will hardly be now denied that all that is to remain as permanent

science in each of these systems must be proved by the examination

of many cases and limited by many conditions and circumstances.

Theories so wide and simple, were consistent only with a

comparatively scanty collection of facts, and belong to the early

stage of geological knowledge. In the progress of the science, the

"theory" of each part of the earth must come out of the examination

of that part, combined with all that is well established, concerning

all the rest; and a general theory must result from the comparison

of all such partial theoretical views. Any attempt to snatch it

before its time must fail; and therefore we may venture at present

to designate general theories, like those of Hutton and Werner, as

_premature_.

This, indeed, is the sentiment of most of the good geologists of the

present day. The time for such general systems, and for the fierce

wars to which the opposition of such generalities gives rise, is

probably now past for ever; and geology will not again witness such

a controversy as that of the Wernerian and Huttonian schools.

. . . . . . As when two black clouds

With heaven's artillery fraught, come rattling on

Over the Caspian: then stand front to front,

Hovering a space, till winds the signal blow

To join their dark encounter in mid-air.

So frowned the mighty combatants, that hell

Grew darker at their frown; so matched they stood:

For never but once more was either like

To meet so great a foe. {586}

The main points really affecting the progress of sound theoretical

geology, will find a place in one of the two next Sections.

[2nd Ed.] [I think I do no injustice to Dr. Hutton in describing his

theory of the earth as _premature_. Prof. Playfair's elegant work,

_Illustrations of the Huttonian Theory_ (1802,) so justly admired,

contains many doctrines which the more mature geology of modern

times rejects; such as the igneous origin of chalk-flints, siliceous

pudding stone, and the like; the universal formation of river-beds

by the rivers themselves; and other points. With regard to this

last-mentioned question, I think all who have read Deluc's

_Geologie_ (1810) will deem his refutation of Playfair complete.

But though Hutton's theory was premature, as well as Werner's, the

former had a far greater value as an important step on the road to

truth. Many of its boldest hypotheses and generalizations have

become a part of the general creed of geologists; and its

publication is perhaps the greatest event which has yet occurred in

the progress of Physical Geology.]

CHAPTER VIII.

THE TWO ANTAGONIST DOCTRINES OF GEOLOGY.

_Sect._ 1.--_Of the Doctrine of Geological Catastrophes._

THAT great changes, of a kind and intensity quite different from the

common course of events, and which may therefore properly be called

_catastrophes_, have taken place upon the earth's surface, was an

opinion which appeared to be forced upon men by obvious facts.

Rejecting, as a mere play of fancy, the notions of the destruction

of the earth by cataclysms or conflagrations, of which we have

already spoken, we find that the first really scientific examination

of the materials of the earth, that of the Sub-Apennine hills, led

men to draw this inference. Leonardo da Vinci, whom we have already

noticed for his early and strenuous assertion of the real marine

origin of fossil impressions of shells, also maintained that the

bottom of the sea had become the top of the mountain; yet his mode

of explaining this may perhaps be claimed by the modern advocates of

uniform causes as more allied to their {587} opinion, than to the

doctrine of catastrophes.[101\18] But Steno, in 1669, approached

nearer to this doctrine; for he asserted that Tuscany must have

changed its face at intervals, so as to acquire six different

configurations, by the successive breaking down of the older strata

into inclined positions, and the horizontal deposit of new ones upon

them. Strabo, indeed, at an earlier period had recourse to

earthquakes, to explain the occurrence of shells in mountains; and

Hooke published the same opinion later. But the Italian geologists

prosecuted their researches under the advantage of having, close at

hand, large collections of conspicuous and consistent phenomena.

Lazzaro Moro, in 1740, attempted to apply the theory of earthquakes

to the Italian strata; but both he and his expositor, Cirillo

Generelli, inclined rather to reduce the violence of these

operations within the ordinary course of nature,[102\18] and thus

leant to the doctrine of uniformity, of which we have afterwards to

speak. Moro was encouraged in this line of speculation by the

extraordinary occurrence, as it was deemed by most persons, of the

rise of a new volcanic island from a deep part of the Mediterranean,

near Santorino, in 1707.[103\18] But in other countries, as the

geological facts were studied, the doctrine of catastrophes appeared

to gain ground. Thus in England, where, through a large part of the

country, the coal-measures are extremely inclined and contorted, and

covered over by more horizontal fragmentary beds, the opinion that

some violent catastrophe had occurred to dislocate them, before the

superincumbent strata were deposited, was strongly held. It was

conceived that a period of violent and destructive action must have

succeeded to one of repose; and that, for a time, some unusual and

paroxysmal forces must have been employed in elevating and breaking

the pre-existing strata, and wearing their fragments into smooth

pebbles, before nature subsided into a new age of tranquillity and

vitality. In like manner Cuvier, from the alternations of

fresh-water and salt-water species in the strata of Paris, collected

the opinion of a series of great revolutions, in which "the thread

of induction was broken." Deluc and others, to whom we owe the first

steps in geological dynamics, attempted carefully to distinguish

between causes now in action, and those which have ceased to act; in

which latter class they reckoned the causes which have {588}

elevated the existing continents. This distinction was assented to

by many succeeding geologists. The forces which have raised into the

clouds the vast chains of the Pyrenees, the Alps, the Andes, must

have been, it was deemed, something very different from any agencies

now operating.

[Note 101\18: "Here is a part of the earth which has become more

light, and which rises, while the opposite part approaches nearer to

the centre, and what was the bottom of the sea is become the top of

the mountain."--Venturi's _Léonardo da Vinci_.]

[Note 102\18: Lyell, i. 3. p. 64. (4th ed.)]

[Note 103\18: Ib. p. 60.]

This opinion was further confirmed by the appearance of a complete

change in the forms of animal and vegetable life, in passing from

one formation to another. The species of which the remains occurred,

were entirely different, it was said, in two successive epochs: a

new creation appears to have intervened; and it was readily believed

that a transition, so entirely out of the common course of the

world, might be accompanied by paroxysms of mechanical energy. Such

views prevail extensively among geologists up to the present time:

for instance, in the comprehensive theoretical generalizations of

Elie de Beaumont and others, respecting mountain-chains, it is

supposed that, at certain vast intervals, systems of mountains,

which may be recognized by the parallelism of course of their

inclined beds, have been disturbed and elevated, lifting up with

them the aqueous strata which had been deposited among them in the

intervening periods of tranquillity, and which are recognized and

identified by means of their organic remains: and according to the

adherents of this hypothesis, these sudden elevations of

mountain-chains have been followed, again and again, by mighty

waves, desolating whole regions of the earth.

The peculiar bearing of such opinions upon the progress of physical

geology will be better understood by attending to the _doctrine of

uniformity_, which is opposed to them, and with the consideration of

which we shall close our survey of this science, the last branch of

our present task.

_Sect._ 2.--_Of the Doctrine of Geological Uniformity._

THE opinion that the history of the earth had involved a serious of

catastrophes, confirmed by the two great classes of facts, the

symptoms of mechanical violence on a very large scale, and of

complete changes in the living things by which the earth had been

tenanted, took strong hold of the geologists of England, France, and

Germany. Hutton, though he denied that there was evidence of a

beginning of the present state of things, and referred many

processes in the formation of strata to existing causes, did not

assert that the elevatory forces which raise continents from the

bottom of the ocean, were of the same order, {589} as well as of the

same kind, with the volcanoes and earthquakes which now shake the

surface. His doctrine of uniformity was founded rather on the

supposed analogy of other lines of speculation, than on the

examination of the amount of changes now going on. "The Author of

nature," it was said, "has not permitted in His works any symptom of

infancy or of old age, or any sign by which we may estimate either

their future or their past duration:" and the example of the

planetary system was referred to in illustration of this.[104\18]

And a general persuasion that the champions of this theory were not

disposed to accept the usual opinions on the subject of creation,

was allowed, perhaps very unjustly, to weigh strongly against them

in the public opinion.

[Note 104\18: Lyell, i. 4, p. 94.]

While the rest of Europe had a decided bias towards the doctrine of

geological catastrophes, the phenomena of Italy, which, as we have

seen, had already tended to soften the rigor of that doctrine, in the

progress of speculation from Steno to Generelli, were destined to

mitigate it still more, by converting to the belief of uniformity

transalpine geologists who had been bred up in the catastrophist

creed. This effect was, indeed, gradual. For a time the distinction of

the _recent_ and the _tertiary_ period was held to be marked and

strong. Brocchi asserted that a large portion of the Sub-Apennine

fossil shells belonged to a living species of the Mediterranean Sea:

but the geologists of the rest of Europe turned an incredulous ear to

this Italian tenet; and the persuasion of the distinction of the

tertiary and the recent period was deeply impressed on most geologists

by the memorable labors of Cuvier and Brongniart on the Paris basin.

Still, as other tertiary deposits were examined, it was found that

they could by no means be considered as contemporaneous, but that they

formed a chain of posts, advancing nearer and nearer to the recent

period. Above the strata of the basins of London and Paris,[105\18]

lie the newer strata of Touraine, of Bourdeaux, of the valley of the

Bormida and the Superga near Turin, and of the basin of Vienna,

explored by M. Constant Prevost. Newer and higher still than these,

are found the Sub-Apennine formations of Northern Italy, and probably

of the same period, the English "crag" of Norfolk and Suffolk. And

most of these marine formations are associated with volcanic products

and fresh-water deposits, so as to imply apparently a long train of

alternations of corresponding processes. It may easily be supposed

that, when the subject had assumed this form, the boundary of the

present and past condition of the earth {590} was in some measure

obscured. But it was not long before a very able attempt was made to

obliterate it altogether. In 1828, Mr. Lyell set out on a geological

tour through France and Italy.[106\18] He had already conceived the

idea of classing the tertiary groups by reference to the number of

recent species which were found in a fossil state. But as he passed

from the north to the south of Italy, he found, by communication with

the best fossil conchologists, Borelli at Turin, Guidotti at Parma,

Costa at Naples, that the number of extinct species decreased; so that

the last-mentioned naturalist, from an examination of the fossil

shells of Otranto and Calabria, and of the neighboring seas, was of

opinion that few of the tertiary shells were of extinct species. To

complete the series of proof, Mr. Lyell himself explored the strata of

Ischia, and found, 2000 feet above the level of the sea, shells, which

were all pronounced to be of species now inhabiting the Mediterranean;

and soon after, he made collections of a similar description on the

flanks of Etna, in the Val di Noto, and in other places.

[Note 105\18: Lyell, 1st ed. vol. iii. p. 61.]

[Note 106\18: 1st ed. vol. iii. Pref.]

The impression produced by these researches is described by

himself.[107\18] "In the course of my tour I had been frequently led

to reflect on the precept of Descartes, that a philosopher should

once in his life doubt everything he had been taught; but I still

retained so much faith in my early geological creed as to feel the

most lively surprize on visiting Sortino, Pentalica, Syracuse, and

other parts of the Val di Noto, at beholding a limestone of enormous

thickness, filled with recent shells, or sometimes with mere casts

of shells, resting on marl in which shells of Mediterranean species

were imbedded in a high state of preservation. All idea of

[necessarily] attaching a high antiquity to a regularly-stratified

limestone, in which the casts and impressions of shells alone were

visible, vanished at once from my mind. At the same time, I was

struck with the identity of the associated igneous rocks of the Val

di Noto with well-known varieties of 'trap' in Scotland and other

parts of Europe; varieties which I had also seen entering largely

into the structure of Etna.

[Note 107\18: Lyell, 1st ed. Pref. x.]

"I occasionally amused myself," Mr. Lyell adds, "with speculating on

the different rate of progress which geology might have made, had it

been first cultivated with success at Catania, where the phenomena

above alluded to, and the great elevation of the modern tertiary beds

in the Val di Noto, and the changes produced in the historical era by

the Calabrian earthquakes, would have been familiarly known." {591}

Before Mr. Lyell entered upon his journey, he had put into the hands

of the printer the first volume of his "Principles of Geology, being

an attempt to explain the former Changes of the Earth's Surface _by

reference to the Causes now in Operation_." And after viewing such

phenomena as we have spoken of, he, no doubt, judged that the

doctrine of catastrophes of a kind entirely different from the

existing course of events, would never have been generally received,

if geologists had at first formed their opinions upon the Sicilian

strata. The boundary separating the present from the anterior state

of things crumbled away; the difference of fossil and recent species

had disappeared, and, at the same time, the changes of position

which marine strata had undergone, although not inferior to those of

earlier geological periods, might be ascribed, it was thought, to

the same kind of earthquakes as those which still agitate that

region. Both the supposed proofs of catastrophic transition, the

organical and the mechanical changes, failed at the same time; the

one by the removal of the fact, the other by the exhibition of the

cause. The powers of earthquakes, even such as they now exist, were,

it was supposed, if allowed to operate for an illimitable time,

adequate to produce all the mechanical effects which the strata of

all ages display. And it was declared that all evidence of a

beginning of the present state of the earth, or of any material

alteration in the energy of the forces by which it has been modified

at various epochs, was entirely wanting.

Other circumstances in the progress of geology tended the same way.

Thus, in cases where there had appeared in one country a sudden and

violent transition from one stratum to the next, it was found, that

by tracing the formations into other countries, the chasm between

them was filled up by intermediate strata; so that the passage

became as gradual and gentle as any other step in the series. For

example, though the conglomerates, which in some parts of England

overlie the coal-measures, appear to have been produced by a

complete discontinuity in the series of changes; yet in the

coal-fields of Yorkshire, Durham, and Cumberland, the transition is

smoothed down in such a way that the two formations pass into each

other. A similar passage is observed in Central-Germany, and in

Thuringia is so complete, that the coal-measures have sometimes been

considered as subordinate to the _todtliegendes_.[108\18]

[Note 108\18: De la Beche, p. 414, _Manual_.]

Upon such evidence and such arguments, the doctrine of {592}

catastrophes was rejected with some contempt and ridicule; and it

was maintained, that the operation of the causes of geological

change may properly and philosophically be held to have been uniform

through all ages and periods. On this opinion, and the grounds on

which it he been urged, we shall make a few concluding remarks.

It must be granted at once, to the advocates of this geological

uniformity, that we are not arbitrarily to assume the existence of

catastrophes. The degree of uniformity and continuity with which

terremotive forces have acted, must be collected, not from any

gratuitous hypothesis, but from the facts of the case. We must

suppose the causes which have produced geological phenomena, to have

been as similar to existing causes, and as dissimilar, as the

effects teach us. We are to avoid all bias in favor of powers

deviating in kind and degree from those which act at present; a bias

which, Mr. Lyell asserts, has extensively prevailed among

geologists.

But when Mr. Lyell goes further, and considers it a merit in a

course of geological speculation that it _rejects_ any difference

between the intensity of existing and of past causes, we conceive

that he errs no less than those whom he censures. "An _earnest and

patient endeavor to reconcile_ the former indication of

change,"[109\18] with _any_ restricted class of causes,--a habit

which he enjoins,--is not, we may suggest, the temper in which

science ought to be pursued. The effects must themselves teach us

the nature and intensity of the causes which have operated; and we

are in danger of error, if we seek for slow and shun violent

agencies further than the facts naturally direct us, no less than if

we were parsimonious of time and prodigal of violence. _Time_,

inexhaustible and ever accumulating his efficacy, can undoubtedly do

much for the theorist in geology; but _Force_, whose limits we

cannot measure, and whose nature we cannot fathom, is also a power

never to be slighted: and to call in the one to protect us from the

other, is equally presumptuous, to whichever of the two our

superstition leans. To invoke Time, with ten thousand earthquakes,

to overturn and set on edge a mountain-chain, should the phenomena

indicate the change to have been sudden and not successive, would be

ill excused by pleading the obligation of first appealing to known

causes.[110\18] {593}

[Note 109\18: Lyell, B. iv. c. i. p. 328, 4th ed.]

[Note 110\18: [2nd Ed.] [I have, in the text, quoted the fourth

edition of Mr. Lyell's _Principles_, in which he recommends "an

earnest and patient endeavor to reconcile the former indications of

change with the evidence of gradual mutation now in progress." In

the sixth edition, in that which is, I presume, the corresponding

passage, although it is transferred from the fourth to the first

Book (B. i. c. xiii. p. 325) he recommends, instead, "an earnest and

patient inquiry how far geological appearances are reconcileable

with the effect of changes now in progress." But while Mr. Lyell has

thus softened the advocate's character in his language in this

passage, the transposition which I have noticed appears to me to

have an opposite tendency. For in the former edition, the causes now

in action were first described in the second and third Books, and

the great problem of Geology, stated in the first Book, was

attempted to be solved in the fourth. But by incorporating this

fourth Book with the first, and thus prefixing to the study of

existing causes arguments against the belief of their geological

insufficiency, there is an appearance as if the author wished his

reader to be prepared by a previous pleading against the doctrine of

catastrophes, before he went to the study of existing causes. The

Doctrines of Catastrophes and of Uniformity, and the other leading

questions of the Palætiological Sciences, are further discussed in

the _Philosophy of the Inductive Sciences_, Book x.]]

In truth, we know causes only by their effects; and in order to

learn the nature of the causes which modify the earth, we must study

them through all ages of their action, and not select arbitrarily

the period in which we live as the standard for all other epochs.

The forces which have produced the Alps and Andes are known to us by

experience, no less than the forces which have raised Etna to its

present height; for we learn their amount in both cases by their

results. Why, then, do we make a merit of using the latter case as a

measure for the former? Or how can we know the true scale of such

force, except by comprehending in our view all the facts which we

can bring together?

In reality when we speak of the _uniformity_ of nature, are we not

obliged to use the term in a very large sense, in order to make the

doctrine at all tenable? It includes catastrophes and convulsions of

a very extensive and intense kind; what is the limit to the violence

which we must allow to these changes? In order to enable ourselves

to represent geological causes as operating with uniform energy

through all time, we must measure our time by long cycles, in which

repose and violence alternate; how long may we extend this cycle of

change, the repetition of which we express by the word _uniformity_?

And why must we suppose that all our experience, geological as well

as historical, includes more than _one_ such cycle? Why must we

insist upon it, that man has been long enough an observer to obtain

the _average_ of forces which are changing through immeasurable

time? {594}

The analogy of other sciences has been referred to, as sanctioning

this attempt to refer the whole train of facts to known causes. To

have done this, it has been said, is the glory of Astronomy: she

seeks no hidden virtues, but explains all by the force of

gravitation, which we witness operating at every moment. But let us

ask, whether it would really have been a merit in the founders of

Physical Astronomy, to assume that the celestial revolutions

resulted from any selected class of known causes? When Newton first

attempted to explain the motions of the moon by the force of

gravity, and failed because the measures to which he referred were

erroneous, would it have been philosophical in him, to insist that

the difference which he found ought to be overlooked, since

otherwise we should be compelled to go to causes other than those

which we usually witness in action? Or was there any praise due to

those who assumed the celestial forces to be the same with gravity,

rather than to those who assimilated them with any other known

force, as magnetism, till the calculation of the laws and amount of

these forces, from the celestial phenomena, had clearly sanctioned

such an identification? We are not to select a conclusion now well

proved, to persuade ourselves that it would have been wise to assume

it anterior to proof, and to attempt to philosophize in the method

thus recommended.

Again, the analogy of Astronomy has been referred to, as confirming

the assumption of perpetual uniformity. The analysis of the heavenly

motions, it has been said, supplies no trace of a beginning, no

promise of an end. But here, also, this analogy is erroneously

applied. Astronomy, as the science of cyclical motions, has nothing

in common with Geology. But look at Astronomy where she has an

analogy with Geology; consider our knowledge of the heavens as a

palætiological science;--as the study of a past condition, from

which the present is derived by causes acting in time. Is there then

no evidence of a beginning, or of a progress? What is the import of

the Nebular Hypothesis? A luminous matter is condensing, solid

bodies are forming, are arranging themselves into systems of

cyclical motion; in short, we have exactly what we are told, on this

analogy, we ought not to have;--the beginning of a world. I will

not, to justify this argument, maintain the truth of the nebular

hypothesis; but if geologists wish to borrow maxims of

philosophizing from astronomy, such speculations as have led to that

hypothesis must be their model.

Or, let them look at any of the other provinces of palætiological

speculation; at the history of states, of civilization, of

languages. We {595} may assume some _resemblance_ or connexion

between the principles which determined the progress of government,

or of society, or of literature, in the earliest ages, and those

which now operate; but who has speculated successfully, assuming an

_identity_ of such causes? Where do we now find a language in the

process of formation, unfolding itself in inflexions, terminations,

changes of vowels by grammatical relations, such as characterize the

oldest known languages? Where do we see a nation, by its natural

faculties, inventing writing, or the arts of life, as we find them

in the most ancient civilized nations? We may assume hypothetically,

that man's faculties develop themselves in these ways; but we see no

such effects produced by these faculties, in our own time, and now

in progress, without the influence of foreigners.

Is it not clear, in all these cases, that history does not exhibit a

series of cycles, the aggregate of which may be represented as a

uniform state, without indication of origin or termination? Does it

not rather seem evident that, in reality, the whole course of the

world, from the earliest to the present times, is but one cycle, yet

unfinished;--offering, indeed, no clear evidence of the mode of its

beginning; but still less entitling us to consider it as a

repetition or series of repetitions of what had gone before?

Thus we find, in the analogy of the sciences, no confirmation of the

doctrine of uniformity, as it has been maintained in Geology. Yet we

discern, in this analogy, no ground for resigning our hope, that

future researches, both in Geology and in other palætiological

sciences, may throw much additional light on the question of the

uniform or catastrophic progress of things, and on the earliest

history of the earth and of man. But when we see how wide and

complex is the range of speculation to which our analogy has

referred us, we may well be disposed to pause in our review of

science;--to survey from our present position the ground that we

have passed over;--and thus to collect, so far as we may, guidance

and encouragement to enable us to advance in the track which lies

before us.

Before we quit the subject now under consideration, we may, however,

observe, that what the analogy of science really teaches us, as the

most promising means of promoting this science, is the strenuous

cultivation of the two subordinate sciences, Geological Knowledge of

Facts, and Geological Dynamics. These are the two provinces of

knowledge--corresponding to Phenomenal Astronomy, and Mathematical

Mechanics--which may lead on to the epoch of the Newton of {596}

geology. We may, indeed, readily believe that we have much to do in

both these departments. While so large a portion of the globe is

geologically unexplored;--while all the general views which are to

extend our classifications satisfactorily from one hemisphere to

another, from one zone to another, are still unformed; while the

organic fossils of the tropics are almost unknown, and their general

relation to the existing state of things has not even been

conjectured;--how can we expect to speculate rightly and securely,

respecting the history of the whole of our globe? And if Geological

Classification and Description are thus imperfect, the knowledge of

Geological Causes is still more so. As we have seen, the necessity

and the method of constructing a science of such causes, are only

just beginning to be perceived. Here, then, is the point where the

labors of geologists may be usefully applied; and not in premature

attempts to decide the widest and abstrusest questions which the

human mind can propose to itself.

It has been stated,[111\18] that when the Geological Society of

London was formed, their professed object was to multiply and record

observations, and patiently to await the result at some future time;

and their favorite maxim was, it is added, that the time was not yet

come for a General System of Geology. This was a wise and

philosophical temper, and a due appreciation of their position. And

even now, their task is not yet finished; their mission is not yet

accomplished. They have still much to do, in the way of collecting

Facts; and in entering upon the exact estimation of Causes, they

have only just thrown open the door of a vast Labyrinth, which it

may employ many generations to traverse, but which they must needs

explore, before they can penetrate to the Oracular Chamber of Truth.

[Note 111\18: Lyell, B. i. c. iv. p. 103.]

I REJOICE, on many accounts, to find myself arriving at the

termination of the task which I have attempted. One reason why I am

glad to close my history is, that in it I have been compelled,

especially in the latter part of my labors, to speak as a judge

respecting eminent philosophers whom I reverence as my Teachers in

those very sciences on which I have had to pronounce a

judgment;--if, indeed, even the appellation of Pupil be not too

presumptuous. But I doubt not that such men are as full of candor

and tolerance, as they are of knowledge and thought. And if they

deem, as I did, that such a history of {597} science ought to be

attempted, they will know that it was not only the historian's

privilege, but his duty, to estimate the import and amount of the

advances which he had to narrate; and if they judge, as I trust they

will, that the attempt has been made with full integrity of

intention and no want of labor, they will look upon the inevitable

imperfections of the execution of my work with indulgence and hope.

There is another source of satisfaction in arriving at this point of

my labors. If, after our long wandering through the region of

physical science, we were left with minds unsatisfied and unraised,

to ask, "Whether this be all?"--our employment might well be deemed

weary and idle. If it appeared that all the vast labor and intense

thought which has passed under our review had produced nothing but a

barren Knowledge of the external world, or a few Arts ministering

merely to our gratification; or if it seemed that the methods of

arriving at truth, so successfully applied in these cases, aid us

not when we come to the higher aims and prospects of our

being;--this History might well be estimated as no less melancholy

and unprofitable than those which narrate the wars of states and the

wiles of statesmen. But such, I trust, is not the impression which

our survey has tended to produce. At various points, the researches

which we have followed out, have offered to lead us from matter to

mind, from the external to the internal world; and it was not

because the thread of investigation snapped in our hands, but rather

because we were resolved to confine ourselves, for the present, to

the material sciences, that we did not proceed onwards to subjects

of a closer interest. It will appear, also, I trust, that the most

perfect method of obtaining speculative truth,--that of which I have

had to relate the result,--is by no means confined to the least

worthy subjects; but that the Methods of learning what is really

true, though they must assume different aspects in cases where a

mere contemplation of external objects is concerned, and where our

own internal world of thought, feeling, and will, supplies the

matter of our speculations, have yet a unity and harmony throughout

all the possible employments of our minds. To be able to trace such

connexions as this, is the proper sequel, and would be the high

reward, of the labor which has been bestowed on the present work.

And if a persuasion of the reality of such connexions, and a

preparation for studying them, have been conveyed to the reader's

mind while he has been accompanying me through our long survey, his

time may not have been employed on {598} these pages in vain.

However vague and hesitating and obscure may be such a persuasion,

it belongs, I doubt not, to the dawning of a better Philosophy,

which it may be my lot, perhaps, to develop more fully hereafter, if

permitted by that Superior Power to whom all sound philosophy

directs our thoughts.

{{599}}

ADDITIONS TO THE THIRD EDITION.

BOOK VIII.

ACOUSTICS.

CHAPTER III.

SOUND.

_The Velocity of Sound in Water._

THE Science of which the history is narrated in this Book has for

its objects, the minute Vibrations of the parts of bodies such as

those by which Sounds are produced, and the properties of Sounds.

The Vibrations of bodies are the result of a certain tension of

their structure which we term _Elasticity_. The Elasticity

determines the rate of Vibration: the rate of Vibration determines

the audible note: the Elasticity determines also the velocity with

which the vibration travels through the substance. These points of

the subject, Elasticity, Rate of Vibration, Velocity of Propagation,

Audible Note, are connected in each substance, and are different in

different substances.

In the history of this Science, considered as tending to a

satisfactory general theory, the Problems which have obviously

offered themselves were, to explain the properties of Sounds by the

relations of their constituent vibrations; and to explain the

existence of vibrations by the elasticity of the substances in which

they occurred: as in Optics, philosophers have explained the

phenomenon of light and colors by the Undulatory Theory, and are

still engaged in explaining the requisite modulations by means of

the elasticity of the Ether. But the _Undulatory Theory of Sound_

was seen to be true at an early period of the Science: and the

explanation, in a general way at least, of all kinds of such

undulations by means of the elasticity of the vibrating substances

has been performed by a series of mathematicians of whom I have

given an account in this Book. Hence the points of the subject

already mentioned (Elasticity, Vibrations and their Propagations,

{600} and Note), have a known material dependence, and each may be

employed in determining the other: for instance, the Note may be

employed in determining the velocity of sound and the elasticity of

the vibrating substance.

Chladni,[1\B] and the Webers,[2\B] had made valuable experimental

inquiries on such subjects. But more complete investigations of this

kind have been conducted with care and skill by M. Wertheim.[3\B]

For instance, he has determined the velocity with which sound

travels in water, by making an organ-pipe to sound by the passage of

water through it. This is a matter of some difficulty; for the

mouthpiece of an organ-pipe, if it be not properly and carefully

constructed, produces sounds of its own, which are not the genuine

musical note of the pipe. And though the note depends mainly upon

the length of the pipe, it depends also, in a small degree, on the

breadth of the pipe and the size of the mouthpiece.

[Note 1\B: _Traité d'Acoustique_, 1809.]

[Note 2\B: _Wellenlehre_, 1852.]

[Note 3\B: _Mémoires de Physique Mécanique_. Paris, 1848.]

If the pipe were a mere line, the time of a vibration would be the

time in which a vibration travels from one end of the pipe to the

other; and thus the note for a given length (which is determined by

the time of vibration), is connected with the velocity of vibration.

He thus found that the velocity of a vibration along the pipe in

sea-water is 1157 _mètres_ per second.

But M. Wertheim conceived that he had previously shown, by general

mathematical reasoning, that the velocity with which sound travels

in an unlimited expanse of any substance, is to the velocity with

which it travels along a pipe or linear strip of the same substance

as the square root of 3 to the square root of 2. Hence the velocity

of sound in sea-water would be 1454 _mètres_ a second. The velocity

of sound in air is 332 _mètres_.