_WORLD-MAKING._
Geological reading, especially when of a strictly uniformitarian
character and in warm weather, sometimes becomes monotonous; and I
confess to a feeling of drowsiness creeping over me when preparing
material for a presidential address to the American Association for the
Advancement of Science in August, 1883. In these circumstances I became
aware of the presence of an unearthly visitor, who announced himself
as of celestial birth, and intimated to me that being himself free
from those restrictions of space and time which are so embarrassing
to earthly students, he was prepared for the moment to share these
advantages with me, and to introduce me to certain outlying parts of
the universe, where I might learn something of its origin and early
history. He took my hand, and instantly we were in the voids of space.
Turning after a moment, he pointed to a small star and said, "That is
the star you call the sun; here, you see, it is only about the third
magnitude, and in a few seconds it will disappear." These few seconds,
indeed, reduced the whole visible firmament to a mere nebulous haze
like the Milky Way, and we seemed to be in blank space. But pausing for
a moment I became aware that around us were multitudes of dark bodies,
so black that they were, so to speak, negatively visible, even in the
almost total darkness around. Some seemed large and massive, some a
mere drift of minute particles, formless and without distinct limits.
Some were swiftly moving, others stationary, or merely revolving on
their own axes. It was a "horror of great darkness," and I trembled
with fear. "This," said my guide, "is what the old Hebrew seer called
_tohu ve bohu_, 'formless and void,' the 'Tiamat' or abyss of the
old Chaldeans, the 'chaos and old night' of the Greeks. Your mundane
physicists have not seen it, but they speculate regarding it, and
occupy themselves with questions as to whether it can be lightened
and vivified by mere attractive force, or by collision of dark bodies
impinging on each other with vast momentum. Their speculations are
vain, and lead to nothing, because they have no data wherefrom to
calculate the infinite and eternal Power who determined either the
attraction or the motion, or who willed which portion of this chaos was
to become cosmos, and which was to remain for ever dead and dark. Let
us turn, however, to a more hopeful prospect." We sped away to another
scene. Here were vast luminous bodies, such as we call nebulæ. Some
were globular, others disc-like, others annular or like spiral wisps,
and some were composed of several concentric shells or rings. All were
in rapid rotation, and presented a glorious and brilliant spectacle.
"This," said my guide, "is matter of the same kind with that we have
just been considering; but it has been set in active motion. The fiat
'Let there be light!' has been issued to it. Nor is its motion in
vain. Each of these nebulous masses is the material of a system of
worlds, and they will produce systems of different forms in accordance
with the various shapes and motions which you observe. Such bodies
are well known to earthly astronomers. One of them, the great nebula
of Andromeda, has been photographed, and is a vast system of luminous
rings of vapour placed nearly edgewise to the earth, and hundreds of
times greater than the whole solar system. But now let us annihilate
time, and consider these gigantic bodies as they will be in the course
of many millions of years." Instantaneously these vast nebulæ had
concentrated themselves into systems of suns and planets, but with
this difference from ours, that the suns were very large and surrounded
with a wide luminous haze, and each of the planets was self-luminous,
like a little sun. In some the planets were dancing up and down in
spiral lines. In others they were moving in one plane. In still others,
in every variety of direction. Some had vast numbers of little planets
and satellites. Others had a few of larger size. There were even
some of these systems that had a pair of central suns of contrasting
colours. The whole scene was so magnificent and beautiful that I
thought I could never weary of gazing on it. "Here," said he, "we have
the most beautiful condition of systems of worlds, when considered from
a merely physical point of view: the perfection of solar and planetary
luminousness, but which is destined to pass away in the interest of
things more important, if less showy. This is the condition of the
great star Sirius, which the old priest astronomers of the Nile Valley
made so much of in their science and religion, and which they called
Sothis. It is now known by your star-gazers to be vastly larger than
your sun, and fifty times more brilliant.[1] Let us select one of these
systems somewhat similar to the solar system, and suppose that the
luminous atmospheres of its nearer planets are beginning to wane in
brilliancy. Here is one of them, through whose halo of light we can see
the body of the planet. What do you now perceive?" The planet referred
to was somewhat larger in appearance than our earth, and, approaching
near to it, I could see that it had a cloud-bearing firmament, and
that it seemed to have continents and oceans, though disposed in more
regular forms than on our own planet, and with a smaller proportion of
land. Looking at it more closely, I searched in vain for any sign of
animal life, but I saw a vast profusion of what might be plants, but
not like those of this world.[2] These were trees of monstrous stature,
and their leaves, which were of great size and shaped like fronds of
seaweeds, were not usually green, but variegated with red, crimson and
orange. The surface of the land looked like beds of gigantic specimens
of _Colias_ and similar variegated-leaved plants, the whole presenting
a most gorgeous yet grotesque spectacle. "This," said my guide, "is the
primitive vegetation which clothes each of the planets in its youthful
state. The earth was once so clothed, in the time when vegetable life
alone existed, and there were no animals to prey upon it, and when the
earth was, like the world you now look upon, a paradise of plants; for
all things in nature are at first in their best estate. This vegetation
is known to you on the earth only by the Carbon and Graphite buried
in your oldest rocks. It still lingers on your neighbour Mars,[3]
which has, however, almost passed beyond this stage, and we are
looking forward before long to see a still more gigantic though paler
development of it in altogether novel shapes on the great continents
that are being formed on the surface of Jupiter. But look again." And
time being again annihilated, I saw the same world, now destitute of
any luminous envelope, with a few dark clouds in its atmosphere, and
presenting just the same appearance which I would suppose our earth
to present to an astronomer viewing it with a powerful telescope from
the moon. "Here we are at home again," said my guide; "good-bye." I
found myself nodding over my table, and that my pen had just dropped
from my hand, making a large blot on my paper. My dream, however, gave
me a hint as to a subject, and I determined to devote my address to a
consideration of questions which geology has not solved, or has only
imperfectly and hypothetically discussed.
[1] In evidence of these and other statements I may refer to Huggins'
recent address as President of the British Association, and to the
"Story of the Heavens," etc., by Sir Robert Ball.
[2] We shall see farther on that there is reason to believe that the
primitive land vegetation was more different from that of the Devonian
and Carboniferous than it is from that of the present day.
[3] Mars is probably a stage behind the earth in its development, and
the ruddy hue of its continents would seem to b: due to some organic
covering.
Such unsolved or partially solved questions must necessarily exist in
a science which covers the whole history of the earth in time. At the
beginning it allies itself with astronomy and physics and celestial
chemistry. At the end it runs into human history, and is mixed up with
archæology and anthropology. Throughout its whole course it has to deal
with questions of meteorology, geography and biology. In short, there
is no department of physical or biological science, with which this
many-sided study is not allied, or at least on which the geologist may
not presume to trespass. When, therefore, it is proposed to discuss
in the present chapter some of the unsolved problems and disputed
questions of this universal science, the reader need not be surprised
if it should be somewhat discursive.
Perhaps we may begin at the utmost limits of the subject by remarking
that in matters of natural and physical science we are met at the
outset with the scarcely solved question as to our own place in the
nature which we study, and the bearing of this on the difficulties
we encounter. The organism of man is decidedly a part of nature. We
place ourselves, in this aspect, in the sub-kingdom vertebrata and
class mammalia, and recognise the fact that man is the terminal link
in a chain of being, extending throughout geological time. But the
organism is not all that belongs to man, and when we regard him as
a scientific inquirer, we raise a new question. If the human mind
is a part of nature, then it is subject to natural law, and nature
includes mind as well as matter. Indeed, without being absolute
idealists we may hold that mind is more potent than matter, and
nearer to the real essence of things. Our science is in any case
necessarily dualistic, being the product of the reaction of mind on
nature, and must be largely subjective and anthropomorphic. Hence,
no doubt, arises much of the controversy of science, and much of the
unsolved difficulty. We recognise this when we divide science into
that which is experimental, or depends on apparatus, and that which is
observational and classificatory--distinctions these which relate not
so much to the objects of science as to our methods of pursuing them.
This view also opens up to us the thought that the domain of science
is practically boundless, for who can set limits to the action of mind
on the universe, or of the universe on mind. It follows that science,
as it exists at any one time, must be limited on all sides by unsolved
mysteries; and it will not serve any good purpose to meet these with
clever guesses. If we so treat the enigmas of the sphinx nature, we
shall surely be devoured. Nor, on the other hand, must we collapse into
absolute despair, and resign ourselves to the confession of inevitable
ignorance. It becomes us rather boldly to confront the unsolved
questions of nature, and to wrestle with their difficulties till we
master such as we can, and cheerfully leave those we cannot overcome to
be grappled with by our successors.
Fortunately, as a geologist, I do not need to invite attention to those
transcendental questions which relate to the ultimate constitution of
matter, the nature of the ethereal medium filling space, the absolute
difference or identity of chemical elements, the cause of gravitation,
the conservation and dissipation of energy, the nature of life, or the
primary origin of bioplasmic matter. I may take the much more humble
_rôle_ of an inquirer into the unsolved or partially solved problems
which meet us in considering that short and imperfect record which
geology studies in the rocky layers of the earth's crust, and which
leads no farther back than to the time when a solid rind had already
formed on the earth, and was already covered with an ocean. This record
of geology covers but a small part of the history of the earth and of
the system to which it belongs, nor does it enter at all into the more
recondite problems involved; still it forms, I believe, some necessary
preparation at least to the comprehension of these. If we are to go
farther back, we must accept the guidance of physicists rather than
of geologists, and I must say that in this physical cosmology both
geologists and general readers are likely to find themselves perplexed
with the vagaries in which the most sober mathematicians may indulge.
We are told that the original condition of the solar system was that
of a vaporous and nebulous cloud intensely heated and whirling rapidly
round, that it probably came into this condition by the impact of two
dark solid bodies striking each other so violently, that they became
intensely heated and resolved into the smallest possible fragments.
Lord Kelvin attributes this impact to their being attracted together
by gravitative force. Croll[4] argues that in addition to gravitation
these bodies must have had a proper motion of great velocity, which
Lord Kelvin thinks "enormously" improbable, as it would require the
solid bodies to be shot against each other with a marvellously true
aim, and this not in the case of the sun only, but of all the stars.
It is rather more improbable than it would be to affirm that in the
artillery practice of two opposing armies, cannon balls have thousands
of times struck and shattered each other midway between the hostile
batteries. The question, we are told, is one of great moment to
geologists, since on the one hypothesis the duration of our system
has amounted to only about twenty millions of years; on the other,
it may have lasted ten times that number.[5] In any case it seems a
strange way of making systems of worlds, that they should result from
the chance collision of multitudes of solid bodies rushing hither
and thither in space, and it is almost equally strange to imagine an
intelligent Creator banging these bodies about like billiard balls in
order to make worlds. Still, in that case we might imagine them not
to be altogether aimless. The question only becomes more complicated
when with Grove and Lockyer we try to reach back to an antecedent
condition, when there are neither solid masses nor nebulæ, but only
an inconceivably tenuous and universally diffused medium made up of an
embryonic matter, which has not yet even resolved itself into chemical
elements. How this could establish any motion within itself tending to
aggregation in masses, is quite inconceivable. To plodding geologists
laboriously collecting facts and framing conclusions therefrom, such
flights of the mathematical mind seem like the wildest fantasies of
dreams. We are glad to turn from them to examine those oldest rocks,
which are to us the foundation stones of the earth's crust.
[4] "Stellar Evolution."
[5] Other facts favour the shorter time (Clarence King, _Am. Jl. of
Science_, vol. xlv., 3rd series).
What do we know of the oldest and most primitive rocks? At this moment
the question may be answered in many and discordant ways; yet the
leading elements of the answer may be given very simply. The oldest
rock formation known to geologists is the Lower Laurentian, the
Fundamental Gneiss, the Lewisian formation of Scotland, the Ottawa
gneiss of Canada, the lowest Archæan crystalline rocks. This formation,
of enormous thickness, corresponds to what the older geologists called
the fundamental granite, a name not to be scouted, for gneiss is only a
stratified or laminated granite. Perhaps the main fact in relation to
this old rock is that it is a gneiss; that is, a rock at once bedded
and crystalline, and having for its dominant ingredient the mineral
orthoclase, a compound of silica, alumina and potash, in which are
imbedded, as in a paste, grains and crystals of quartz and hornblende.
We know very well from its texture and composition that it cannot be
a product of mere heat, and being a bedded rock we infer that it was
laid down layer by layer in the manner of aqueous deposits. On the
other hand, its chemical composition is quite different from that
of the muds, sands and gravels usually deposited from water. Their
special characters are caused by the fact that they have resulted from
the slow decay of rocks like these gneisses, under the operation of
carbon dioxide and water, whereby the alkaline matter and the more
soluble part of the silica have been washed away, leaving a residue
mainly silicious and aluminous.[6] Such more modern rocks tell of dry
land subjected to atmospheric decay and ram-wash. If they have any
direct relation to the old gneisses, they are their grandchildren, not
their parents. On the contrary, the oldest gneisses show no pebbles or
sand or limestone--nothing to indicate that there was then any land
undergoing atmospheric waste, or shores with sand and gravel. For
all that we know to the contrary, these old gneisses may have been
deposited in a shoreless sea, holding in solution or suspension merely
what it could derive from a submerged crust recently cooled from a
state of fusion, still thin, and exuding here and there through its
fissures heated waters and volcanic products. This, it may be observed
here, is just what we have a right to expect, if the earth was once a
heated or fluid mass, and if our oldest Laurentian rocks consist of
the first beds or layers deposited upon it, perhaps by a heated ocean.
It has been well said that "the secret of the earth's hot youth has
been well kept." But with the help of physical science we can guess at
an originally heat-liquefied ball with denser matter at its centre,
lighter and oxidised matter at its surface. We can imagine a scum or
crust forming at the surface; and from what we know of the earth's
interior, nothing is more likely to have constituted that slaggy crust
than the material of our old gneisses. As to its bedded character,
this may have arisen in part from the addition of cooling layers
below, in part from the action of heated water above, and in part from
pressure or tension; while, wherever it cracked or became broken, its
interstices would be injected with molten matter from beneath. All this
may be conjecture, but it is based on known facts, and is the only
probable conjecture. If correct, it would account for the fact that the
gneissic rocks are the lowest and oldest that we reach in every part of
the earth.
[6] Carbon dioxide, the great agent in the decay of silicious rocks,
must then have constituted a very much larger part of the atmosphere
than at present.
In short, the fundamental gneiss of the Lower Laurentian may have
been the first rock ever formed; and in any case it is a rock formed
under conditions which have not since recurred, except locally. It
constitutes the first and best example of those chemico-physical,
aqueous or aqueo-igneous rocks, so characteristic of the earliest
period of the earth's history. Viewed in this way the Lower Laurentian
gneiss is probably the oldest kind of rock we shall ever know the limit
to our backward progress, beyond which there remains nothing to the
geologist except physical hypotheses respecting a cooling incandescent
globe. For the chemical conditions of these primitive rocks, and what
is known as to their probable origin, I may refer to the writings of
my friends, the late Dr. Sterry Hunt and Dr. J. G. Bonney, to whom we
owe so much of what is known of the older crystalline rocks[7] as well
as of their literature, and the questions which they raise. My purpose
here is to sketch the remarkable difference which we meet as we ascend
into the Middle and Upper Laurentian.
[7] Hunt, "Essays on Chemical Geology"; Bonney, "Addresses to British
Association and Geological Society of London."
In the next succeeding formation, the middle part of the Laurentian
of Logan, the Grenville series of Canada, we meet with a great and
significant change. It is true we have still a predominance of
gneisses which may have been formed in the same manner with those
below them; but we find these now associated with great beds of
limestone and dolomite, which must have been formed by the separation
of calcium and magnesium carbonates from the sea water, either by
chemical precipitation or by the agency of living beings. We have also
quartzite, quartzose gneisses, and even pebble beds, which inform us
of sandbanks and shores. Nay, more, we have beds containing graphite
which must be the residue of plants, and iron ores which tell of the
deoxidation of iron oxide by organic matters. In short, here we have
evidence of new factors in world-building, of land and ocean, of
atmospheric decay of rocks, of deoxidizing processes carried on by
vegetable life on the land and in the waters, of limestone-building in
the sea. To afford material for such rocks, the old Ottawa gneiss must
have been lifted up into continents and mountain masses by bendings
and foldings of the original crust. Under the slow but sure action of
the carbon dioxide dissolved in rainwater, its felspar had crumbled
down in the course of ages. Its potash, soda, lime, magnesia, and part
Of its silica had been washed into the sea, there to enter into new
combinations and to form new deposits. The crumbling residue of fine
clay and sand had been also washed down into the borders of the ocean,
and had been there deposited in beds. Thus the earth had entered into
a new phase, which continues onward through the geological ages; and I
place in the reader's hands one key for unlocking the mystery of the
world in affirming that this great change took place, this new era was
inaugurated in the midst of the Laurentian period, the oldest of our
great divisions of the earth's geological history.[8]
[8] I follow the original arrangement of Logan, who first defined this
succession in the extensive and excellent exposures of these rocks in
Canada. Elsewhere the subject has often been confused and mixed with
local details. The same facts, though sometimes under different names,
are recorded by the geologists of Scandinavia, Britain, and the United
States, and the acceptance of the conclusions of Nicol and Lapworth has
served to bring even the rocks of the Highlands of Scotland more into
line with those of Canada.
Was not this a fit period for the first appearance of life? should we
not expect it to appear, independently of the evidence of the fact, so
soon at least as the temperature of the ocean falls sufficiently low
to permit its existence?[9] I do not propose to enter here into that
evidence. This we shall have occasion to consider in the sequel. I
would merely say here that we should bear in mind that in this latter
half of the Lower Laurentian, or if we so choose to style it, Middle
Laurentian period, we have the conditions required for life in the
sea and on the land; and since in other periods we know that life was
always present when its conditions were present, it is not unreasonable
to look for the earliest traces of life in this formation, in which we
find, for the first time, the completion of those physical arrangements
which make life, in such forms of it as exist in the sea, possible.
[9] Dana states this at 180°F. for plants and 120° for animals.
This is also a proper place to say something of the disputed doctrine
of what is termed metamorphism, or the chemical and molecular changes
which old rocks have undergone.
The Laurentian rocks are undoubtedly greatly changed from their
original state, more especially in the matters of crystallization and
the formation of disseminated minerals, by the action of heat and
heated water. Sandstones have thus passed into quartzites, clays into
slates and schists, limestones into marbles. So far, metamorphism is
not a doubtful question; but when theories of metamorphism go so far as
to suppose an actual change of one element for another, they go beyond
the bounds of chemical credibility; yet such theories of metamorphism
are often boldly advanced and made the basis of important conclusions.
Dr. Hunt has happily given the name "metasomatosis" to this imaginary
and improbable kind of metamorphism. I would have it to be understood
that, in speaking of the metamorphism of the older crystalline rocks,
it is not to this metasomatosis that I refer, and that I hold that
rocks which have been produced out of the materials decomposed by
atmospheric erosion can never by any process of metamorphism be
restored to the precise condition of the Laurentian rocks. Thus,
there is in the older formations a genealogy of rocks, which, in the
absence of fossils, may be used with some confidence, but which does
not apply to the more modern deposits, and which gives a validity to
the use of mineral character in classifying older rocks which does
not hold for later formations. Still, nothing in geology absolutely
perishes, or is altogether discontinued; and it is probable that,
down to the present day, the causes which produced the old Laurentian
gneiss may still operate in limited localities. Then, however, they
were general, not exceptional. It is further to be observed that the
term gneiss is sometimes of wide and even loose application. Beside the
typical orthoclase and hornblendic gneiss of the Laurentian, there are
micaceous, quartzose, garnetiferous and many other kinds of gneiss; and
even gneissose rocks, which hold labradorite or anorthite instead of
orthoclase, are sometimes, though not accurately, included in the term.
The Grenville series, or Middle Laurentian, is succeeded by what Logan
in Canada called the Upper Laurentian, and which other geologists have
called the Norite or Norian series. Here we still have our old friends
the gneisses, but somewhat peculiar in type, and associated with
them are great beds and masses, rich in lime-felspar, the so-called
labradorite and anorthite rocks. The precise 'origin of these is
uncertain, but this much seems clear, namely, that they originated in
circumstances in which the great limestones deposited in the Lower or
Middle Laurentian were beginning to be employed in the manufacture,
probably by aqueo-igneous agencies, of lime-felspars. This proves the
Norian rocks to be younger than the Lower Laurentian, and that, as
Logan supposed, considerable earth-movements had occurred between the
two, implying lapse of time, while it is also evident that the folding
and crumpling of the Lower Laurentian had led to great outbursts of
igneous matter from below the crust, or from its under part.
Next to the Laurentian, but probably after an interval, the rocks
of which are yet scarcely known, we have the Huronian of Logan, a
series much less crystalline and more fragmentary, and affording more
evidence of land elevation and atmospheric and aqueous erosion than
those preceding it. It has extensive beds of volcanic rock, great
conglomerates, some of them made up of rounded fragments of Laurentian
rocks, and others of quartz pebbles, which must have been the remains
of rocks subjected to very perfect decay. The pure quartz-rocks tell
the same tale, while slates and limestones speak also of chemical
separation of the materials of older rocks. The Huronian evidently
tells of previous movements in the Laurentian, and changes which
allowed the Huronian to be deposited along its shores and on the edges
of its beds. Yet the Huronian itself is older than the Palæozoic
series, and affected by powerful earth-movements at an earlier date.
Life existed in the waters in Huronian times. We have spicules of
sponges in the limestone, and organic markings on the slaty beds; but
they are few, and their nature is uncertain.
Succeeding the Huronian, and made up of its _débris_ and that of the
Laurentian, we have the great Cambrian series, that in which we first
find undoubted evidence of abundant marine life, and which thus forms
the first chapter in the great Palæozoic book of the early history of
the world. Here let it be observed we have at least two wide gaps in
our history, marked by the crumpling up, first, of the Laurentian, and
then of the Huronian beds.
After what has been said, the reader will perhaps not be astonished
that fierce geological battles have raged over the old crystalline
rocks. By some geologists they are almost entirely explained away,
or referred to igneous action, or to the alteration of ordinary
sediments. Under the treatment of another school they grow to great
series of Pre-Cambrian rocks, constituting vast systems of formations,
distinguishable from each other chiefly by differences of mineral
character. Facts and fossils are daily being discovered, by which these
disputes will ultimately be settled.
After the solitary appearance of Eozoon in the Laurentian, and of a few
uncertain forms in the Huronian, we find ourselves, in the Cambrian,
in the presence of a nearly complete invertebrate fauna of protozoa,
polyps, echinoderms, mollusks and Crustacea, and this not confined to
one locality merely, but apparently extended simultaneously throughout
the ocean, over the whole world. This sudden incoming of animal
life, along with the subsequent introduction of successive groups of
invertebrates, and finally of vertebrate animals, furnishes one of
the greatest unsolved problems of geology, which geologists were wont
to settle by the supposition of successive creations. In the sequel
I shall endeavour to set forth the facts as to this succession, and
the general principles involved in it, and to show the insufficiency
of certain theories of evolution suggested by biologists to give any
substantial aid to the geologist in these questions. At present I
propose merely to notice some of the general principles which should
guide us in studying the development of life in geological time, and
the causes which have baffled so many attempts to throw light on this
obscure portion of our unsolved problems.
It has been urged on the side of rational evolution--and there are both
rational and irrational forms of this many-sided doctrine--that this
hypothesis does not profess to give an explanation of the absolute
origin of life on our planet, or even of the original organization of
a single cell, or of a simple mass of protoplasm, living or dead. All
experimental attempts to produce by synthesis the complex albuminous
substances, or to obtain the living from the non-living, have so far
been fruitless, and indeed we cannot imagine any process by which such
changes could be effected. That they have been effected we know, but
the process employed by their maker is still as mysterious to us as it
probably was to him who wrote the words:--"And God said, Let the waters
swarm with swarmers." How vast is the gap in our knowledge and our
practical power implied in this admission, which must, however, be made
by every mind not absolutely blinded by a superstitious belief in those
forms of words which too often pass current as philosophy.
But if we are content to start with a number of organisms ready made--a
somewhat humiliating start, however--we still have to ask--How do
these vary so as to give new species? It is a singular illusion, and
especially in the case of men who profess to be believers in natural
law, that variation may be boundless, aimless and fortuitous, and
that it is by spontaneous selection from varieties thus produced that
development arises. But surely the supposition of mere chance and
magic is unworthy of science. Varieties must have causes, and their
causes and their effects must be regulated by some law or laws. Now it
is easy to see that they cannot be caused by a mere innate tendency
in the organism itself. Every organism is so nicely equilibrated that
it has no such spontaneous tendency, except within the limits set by
its growth and the law of its periodical changes. There may, however,
be equilibrium more or less stable. I believe all attempts hitherto
made have failed to account for the fixity of certain, nay, of very
many, types throughout geological time, but the mere consideration
that one may be in a more stable state of equilibrium than another,
so far explains it. A rocking stone has no more spontaneous tendency
to move than an ordinary boulder, but it may be made to move with a
touch. So it probably is with organisms. But if so, then the causes of
variation are external, as in many cases we actually know them to be,
and they must depend on instability with change in surroundings, and
this so arranged as not to be too extreme in amount, and to operate
in some determinate direction. Observe how remarkable the unity of
the adjustments involved in such a supposition!--how superior they
must be to our rude and always more or less unsuccessful attempts to
produce and carry forward varieties and races in definite directions!
This cannot be chance. If it exists, it must depend on plans deeply
laid in the nature of things, else it would be most monstrous magic
and causeless miracle. Still more certain is this conclusion when we
consider the vast and orderly succession made known to us by geology,
and which must have been regulated by fixed laws, only a few of which
are as yet known to us.
Beyond these general considerations we have others of a more special
character, based on palæontological facts, which show how imperfect are
our attempts as yet to reach the true causes of the introduction of
genera and species.
One is the remarkable fixity of the leading types of living beings
in geological time. If, instead of framing, like Haeckel, fanciful
phylogenies, we take the trouble, with Barrande and Gaudry, to trace
the forms of life through the period of their existence, each along its
own line, we shall be greatly struck with this, and especially with the
continuous existence of many low types of life through vicissitudes of
physical conditions of the most stupendous character, and over a lapse
of time scarcely conceivable. What is still more remarkable is that
this holds in groups which, within certain limits, are perhaps the most
variable of all. In the present world no creatures are individually
more variable than the protozoa; as, for example, the foraminifera and
the sponges. Yet these groups are fundamentally the same, from the
beginning of the Palæozoic until now, and modern species seem scarcely
at all to differ from specimens procured from rocks at least half-way
back to the beginning of our geological record. If we suppose that the
present sponges and foraminifera are the descendants of those of the
Silurian period, we can affirm that in all that vast lapse of time they
have, on the whole, made little greater change than that which may be
observed in variable forms at present. The same remark applies to other
low animal forms. In types somewhat higher and less variable, this is
almost equally noteworthy. The pattern of the venation of the wings of
cockroaches, and the structure and form of land snails, gally-worms and
decapod crustaceans were all settled in the Carboniferous age, in a way
that still remains. So were the foliage and the fructification of club
mosses and ferns. If, at any time, members of these groups branched
off, so as to lay the foundation of new species, this must have been
a very rare and exceptional occurrence, and one demanding even some
suspension of the ordinary laws of nature.
We may perhaps be content on this question to say with Gaudry,[10]
that it is not yet possible to "pierce the mystery that surrounds
the development of the great classes of animals," or with Prof.
Williamson,[11] that in reference to fossil plants "the time has
not yet arrived for the appointment of a botanical King-at-arms and
Constructor of pedigrees." We shall, however, find that by abandoning
mere hypothetical causes and carefully noting the order of the
development and the causes in operation, so far as known, we may reach
to ideas as to cause and mode, and the laws of succession, even if
unable to penetrate the mystery of origins.
[10] "Enchainements du Monde Animal," Paris, 1883.
[11] Address before Royal Institution, Feb., 1883.
Another caution which a palæontologist has occasion to give with regard
to theories of life, has reference to the tendency of biologists to
infer that animals and plants were introduced under embryonic forms,
and at first in few and imperfect species. Facts do not substantiate
this. The first appearance of leading types of life is rarely
embryonic, or of the nature of immature individuals. On the contrary,
they often appear in highly perfect and specialized forms, often,
however, of composite type and expressing characters afterwards so
separated as to belong to higher groups. The trilobites of the Cambrian
are some of them of few segments, and so far embryonic, but the greater
part are many-segmented and very complex. The batrachians of the
Carboniferous present many characters higher than those of their modern
successors and now appropriated to the true reptiles. The reptiles of
the Permian and Trias usurped some of the prerogatives of the mammals.
The ferns, lycopods and equisetums of the Devonian and Carboniferous
were, in fructification, not inferior to their modern representatives,
and in the structure of their stems far superior. The shell-bearing
cephalopods of the Palæozoic would seem to have possessed structures
now special to a higher group, that of the cuttle-fishes. The bald and
contemptuous negation of these facts by Haeckel and other biologists
does not tend to give geologists much confidence in their dicta.
Again, we are now prepared to say that the struggle for existence,
however plausible as a theory, when put before us in connection
with the productiveness of animals and the few survivors of their
multitudinous progeny, has not been the determining cause of the
introduction of new species. The periods of rapid introduction
of new forms of marine life were not periods of struggle, but of
expansion--those periods in which the submergence of continents
afforded new and large space for their extension and comfortable
subsistence. In like manner, it was continental emergence that afforded
the opportunity for the introduction of land animals and plants.
Further, in connection with this, it is now an established conclusion
that the great aggressive faunas and floras of the continents have
originated in the north, some of them within the arctic circle, and
this in periods of exceptional warmth, when the perpetual summer
sunshine of the arctic regions coëxisted with a warm temperature.
The testimony of the rocks thus is that not struggle but expansion
furnished the requisite conditions for new forms of life, and that the
periods of struggle were characterized by depauperation and extinction.
But we are sometimes told that organisms are merely mechanical, and
that the discussions respecting their origin have no significance any
more than if they related to rocks or crystals, because they relate
merely to the organism considered as a machine, and not to that which
may be supposed to be more important, namely, the great determining
power of mind and will. That this is a mere evasion by which we
really gain nothing, will appear from a characteristic extract of an
article by an eminent biologist in the new edition of the Encyclopedia
Britannica, a publication which, I am sorry to say, instead of its
proper _rôle_ as a repertory of facts, has admitted partisan papers,
stating extreme and unproved speculations as if they were conclusions
of science. The statement referred to is as follows:--"A mass of living
protoplasm is simply a molecular machine of great complexity, the total
results of the working of which, or its vital phenomena, depend on the
one hand on its construction, and on the other, on the energy supplied
to it; and to speak of vitality as anything but the name for a series
of operations is as if one should talk of the horologity of a clock."
It would, I think, scarcely be possible to put into the same number
of words a greater amount of unscientific assumption and unproved
statement than in this sentence. Is "living protoplasm" different in
any way from dead protoplasm, and if so, what causes the difference?
What is a "machine"? Can we conceive of a self-produced or uncaused
machine, or one not intended to work out some definite results? The
results of the machine in question are said to be "vital phenomena";
certainly most wonderful results, and greater than those of any machine
man has yet been able to construct. But why "vital"? If there is no
such thing as life, surely they are merely physical results. Can
mechanical causes produce other than physical effects? To Aristotle
life was "the cause of form in organisms." Is not this quite as likely
to be true as the converse proposition? If the vital phenomena depend
on the "construction" of the machine, and the "energy supplied to it,"
whence this construction and whence this energy? The illustration of
the clock does not help us to answer this question. The construction of
the clock depends on its maker, and its energy is derived from the hand
that winds it up. If we can think of a clock which no one has made, and
which no one winds, a clock constructed by chance, set in harmony with
the universe by chance, wound up periodically by chance, we shall then
have an idea parallel to that of an organism living, yet without any
vital energy or creative law; but in such a case we should certainly
have to assume some antecedent cause, whether we call it "horologity"
or by some other name. Perhaps the term evolution would serve as well
as any other, were it not that common sense teaches that nothing can be
spontaneously evolved out of that in which it did not previously exist.
There is one other unsolved problem in the study of life by the
geologist to which it is still necessary to advert. This is the
inability of palæontology to fill up the gaps in the chain of being.
In this respect we are constantly taunted with the imperfection of the
record, a matter so important that it merits a separate treatment; but
facts show that this is much more complete than is generally supposed.
Over long periods of time and many lines of being we have a nearly
continuous chain, and if this does not show the tendency desired,
the fault is as likely to be in the theory as in the record. On the
other hand, the abrupt and simultaneous appearance of new types in
many specific and generic forms and over wide and separate areas at
one and the same time, is too often repeated to be accidental. Hence
palæontologists, in endeavouring to establish evolution, have been
obliged to assume periods of exceptional activity in the introduction
of species, alternating with others of stagnation, a doctrine differing
very little from that of special creation, as held by the older
geologists.
The attempt has lately been made to account for these breaks by the
assumption that the geological record relates only to periods of
submergence, and gives no information as to those of elevation. This
is manifestly untrue. In so far as marine life is concerned, the
periods of submergence are those in which new forms abound for very
obvious reasons, already hinted; but the periods of new forms of land
and fresh-water life are those of elevation, and these have their own
records and monuments, often very rich and ample, as, for example, the
swamps of the Carboniferous, the transition from the great Cretaceous
subsidence, when so much of the land of the Northern Hemisphere
was submerged, to the new continents of the Tertiary, the Tertiary
lake-basins of Western America, the Terraces and raised beaches of
the Pleistocene. Had I time to refer in detail to the breaks in the
continuity of life which cannot be explained by the imperfection of the
record, I could show at least that nature in this case does advance
_per saltum_--by leaps, rather than by a slow continuous process. Many
able reasoners, as Le Conte, in America, and Mivart and Collard in
England, hold this view.
Here, as elsewhere, a vast amount of steady conscientious work is
required to enable us to solve the problems of the history of life. But
if so, the more the hope for the patient student and investigator. I
know nothing more chilling to research, or unfavourable to progress,
than the promulgation of a dogmatic decision that there is nothing to
be learned but a merely fortuitous and uncaused succession, amenable
to no law, and only to be covered, in order to hide its shapeless and
uncertain proportions, by the mantle of bold and gratuitous hypothesis.
So soon as we find evidence of continents and oceans we raise the
question, Have these continents existed from the first in their present
position and form, or have the land and water changed places in the
course of geological time? This question also deserves a separate and
more detailed consideration. In reality both statements are true in a
certain limited sense. On the one hand, any geological map whatever
suffices to show that the general outline of the existing land began to
be formed in the first and oldest crumplings of the crust. On the other
hand, the greater part of the surface of the land consists of marine
sediments which must have been deposited when the continents were
in great part submerged, and whose materials must have been derived
from land that has perished in the process, while all the continental
surfaces, except, perhaps, some high peaks and ridges, have been many
times submerged. Both of these apparently contradictory statements
are true; and without assuming both, it is impossible to explain the
existing contours and reliefs of the surface.
In exceptional cases even portions of deep sea have been elevated, as
in the case of the Polycistine deposits in the West Indies; but these
exceptions are as yet scarcely sufficient to prove the rule.
In the case of North America, the form of the old nucleus of Laurentian
rock in the north already marks out that of the finished continent, and
the successive later formations have been laid upon the edges of this,
like the successive loads of earth dumped over an embankment. But in
order to give the great thickness of the Palæozoic sediments, the land
must have been again and again submerged, and for long periods of time.
Thus, in one sense, the continents have been fixed; in another, they
have been constantly fluctuating. Hall and Dana have well illustrated
these points in so far as eastern North America is concerned. Prof.
Hull of the Geological Survey of Ireland has had the boldness to
reduce the fluctuations of land and water, as evidenced in the British
Islands, to the form of a series of maps intended to show the physical
geography of each successive period. The attempt is probably premature,
and has been met with much adverse criticism; but there can be no
doubt that it has an element of truth. When we attempt to calculate
what could have been supplied from the old Eozoic nucleus by decay
and aqueous erosion, and when we take into account the greater local
thickness of sediments towards the present sea-basins, we can scarcely
avoid the conclusion that extensive areas once occupied by high land
are now under the sea. But to ascertain the precise areas and position
of these perished lands may now be impossible.
In point of fact we are obliged to believe in the contemporaneous
existence in all geological periods, except perhaps the very oldest, of
three sorts of areas on the surface of the earth: (1) Oceanic areas of
deep sea, which must always have occupied the bed of the present ocean,
or parts of it; (2) Continental plateaus sometimes existing as low
flats, or as higher table-lands, and sometimes submerged; (3) Areas of
plication or folding, more especially along the borders of the oceans,
forming elevated lands rarely submerged and constantly affording the
material of sedimentary accumulations. We shall find, however, that
these have changed places in a remarkable manner, though always in such
a way that neither the life of the land nor of the waters was wholly
extinguished in the process.
Every geologist knows the contention which has been occasioned by the
attempts to correlate the earlier Palæozoic deposits of the Atlantic
margin of North America with those forming at the same time on the
interior plateau, and with those of intervening lines of plication and
igneous disturbance. Stratigraphy, lithology and fossils are all more
or less at fault in dealing with these questions, and while the general
nature of the problem is understood by many geologists, its solution
in particular cases is still a source of apparently endless debate.
The causes and mode of operation of the great movements of the earth's
crust which have produced mountains, plains and table-lands, are still
involved in some mystery. One patent cause is the unequal settling of
the crust towards the centre; but it is not so generally understood
as it should be, that the greater settlement of the ocean-bed has
necessitated its pressure against the sides of the continents in
the same manner that a huge ice-floe crushes a ship or a pier. The
geological map of North America shows this at a glance, and impresses
us with the fact that large portions of the earth's crust have not only
been folded but bodily pushed back for great distances. On looking at
the extreme north, we see that the great Laurentian mass of central
Newfoundland has acted as a projecting pier to the space immediately
west of it, and has caused the gulf of St. Lawrence to remain an
undisturbed area since Palæozoic times. Immediately to the south of
this, Nova Scotia and New Brunswick are folded back. Still farther
south, as Guyot has shown, the old sediments have been crushed in sharp
folds against the Adirondack mass, which has sheltered the table-land
of the Catskills and of the great lakes. South of this again the rocks
of Pennsylvania and Maryland have been driven back in a great curve
to the west. Movements of this kind on the Pacific coast of America
have been still more stupendous, as well as more recent. Dr. G. M.
Dawson[12] thus refers to the crushing action of the Pacific bed on
the rocks of British Columbia, and this especially at two periods, the
close of the Triassic and the close of the Cretaceous: "The successive
foldings and crushings which the Cordillera region has suffered have
resulted in an actual change of position of the rocks now composing
its western margin. This change may have amounted since the beginning
of Mesozoic time to one-third of its whole present width, which would
place the line of the coast ranges about two degrees of longitude
farther west." Here we have evidence that a tract of country 400
miles wide and consisting largely of mountain ranges and table-lands,
has been crushed bodily back over two degrees of longitude; and this
applies not to British Columbia merely, but to the whole west coast
from Alaska to Chili. Yet we know that any contraction of the earth's
nucleus can crumple up only a very thin superficial crust, which in
this case must have slid over the pasty mass below.[13] Let it be
observed, however, that the whole lateral pressure of vast areas
has been condensed into very narrow lines. Nothing, I think, can
more forcibly show the enormous pressure to which the edges of the
continents have been exposed, and at the same time the great sinking of
the hard and resisting ocean-beds. Complex and difficult to calculate
though these movements of plication are, they are more intelligible
than the apparently regular pulsations of the flat continental areas,
whereby they have alternately been below and above the waters, and
which must have depended on somewhat regularly recurring causes,
connected either with the secular cooling of the earth or with the
gradual retardation of its rotation, or with both. There is, however,
good reason to believe that the successive subsidences alternated with
the movements of plication, and depended on upward bendings of the
ocean floor, and also on the gradual slackening of the rotation of the
earth. Throughout these changes, each successive elevation exposed the
rocks for long ages to the decomposing influence of the atmosphere.
Each submergence swept away and deposited as sediment the material
accumulated by decay. Every change of elevation was accompanied with
changes of climate, and with modifications of the habitats of animals
and plants. Were it possible to restore accurately the physical
geography of the earth in all these respects, for each geological
period, the data for the solution of many difficult questions would be
furnished.
[12] Trans. Royal Society of Canada, 1890.
[13] This view is quite consistent with the practical solidity of the
earth, and with the action of local expansion by heat, of settlement of
areas overloaded with sediment, and of downward sliding of beds. This
we shall see in the sequel.
We have wandered through space and time sufficiently for one chapter,
and some of the same topics must come up later in other connections.
Let us sum up in a word. In human history we are dealing with the
short lives and limited plans of man. In the making of worlds we are
conversant with the plans of a Creator with whom one day is as a
thousand years, and a thousand years as one day. We must not measure
such things by our microscopic scale of time. Nor should we fail to
see that vast though the ages of the earth are, they are parts of a
continuous plan, and of a plan probably reaching in space and time
immeasurably beyond our earth. When we trace the long history from an
incandescent fire-mist to a finished earth, and vast ages occupied by
the dynasties of plant and animal life, we see not merely a mighty
maze, an almost endless procession of changes, but that all of these
were related to one another by a chain of causes and effects leading
onward to greater variety and complexity, while retaining throughout
the traces of the means employed. The old rocks and the ancient lines
of folding and the perished forms of life are not merely a scaffolding
set up to be thrown down, but the foundation stones of a great and
symmetrical structure. Is it yet completed? Who can tell? The earth may
still be young, and infinite ages of a better history may lie before it.
References[14]:--Presidential Address to the American Association
for the Advancement of Science, meeting at Minneapolis, 1883. "The
Story of the Earth and Man." Ninth edition, London, 1887.
[14] The references in this and succeeding chapters are exclusively
to papers and works by the author, on which the several chapters are
based.
_THE IMPERFECTION OF THE GEOLOGICAL RECORD._
DEDICATED TO THE MEMORY OF
JOACHIN BARRANDE,
One of the most successful Labourers
in the Completion of the History
of Life in its earlier Stages.
Nature of the Imperfection--Questions as to its arising from
Want of Continuity, from Lack of Preservation, from Imperfect
Collecting.--Examples--Land Snails, Carboniferous Batrachians,
Palæozoic Sponges, Pleistocene Shells, Devonian and Carboniferous
Plants--Comparative Perfection in the Case of Marine Shells,
etc.--Possible Cambrian Squids--Questions as to Want of First Chapters
of the Record--Practical Conclusions
[Illustration: Cambro-Silurian Sponges restored.--_Protospongia_,
_Acanthodictya_, _Cyathospongia_, _Lasiothrix_, _Halichondrites_,
Palæosaccus, etc., from a single bed of shale in the Quebec Group,
Little Metis, Canada (p. 47).]