+---------------------------------------+---------------+--------------+
| | ANIMAL | VEGETABLE |
| GEOLOGICAL PERIODS. | LIFE. | LIFE. |
+---------------------------------------+---------------+--------------+
| | | |
| CAINOZOIC or NEOZOIC. | | |
| | Age of _Man_ | |
| { _Post- { Recent. | and _Modern | |
| { Tertiary_ { Post-Glacial. | Mammals_. | |
| { or _Modern_ | | Age of |
| { |Age of _Extinct|_Angiosperms_ |
| { { Pleistocene, or | Mammals_. | and _Palms_. |
| { _Tertiary_ { Pliocene. | (Earliest | |
| { { Miocene. | Placental | |
| { { Eocene. | Mammals.) | |
| | | |
+---------------------------------------+---------------+--------------+
| | | |
| MESOZOIC. | | |
| { { Upper, | | (Earliest |
| { _Cretaceous_ { Lower, or Neocomian. | | Modern |
| { | Age of | Trees.) |
| { | _Reptiles_ | |
| { { Oolite. | and _Birds_. | |
| { _Jurassic_ { Lias. | | Age of |
| { | | _Cycads_ and |
| { { Upper, | (Earliest | _Pines_. |
| { _Triassic_ { Middle, or | Marsupial | |
| { { Muschelkalk. | Mammals.) | |
| { { Lower. | | |
| | | |
+---------------------------------------+---------------+--------------+
| | | |
| PALÆOZOIC. | | |
| { { Upper, | | |
| { { Middle, or Magnesian | | |
| { _Permian_ { Limestone. |(Earliest True | |
| { { Lower. | Reptiles.) | |
| { | | |
| { { Upper Coal-Formation.| | |
| { _Carboni- { Coal-Formation. | | |
| { ferous_ { Carboniferous | | |
| { { Limestone. | | |
| { { Lower Coal-Formation.| Age of | Age of |
| { | _Amphibians_ |_Acrogens_ and|
| { _Erian_ { Upper. | and _Fishes_. |_Gymnosperms_.|
| { or { Middle. | | |
| { _Devonian_ { Lower. | | |
| { | | |
| { { Upper, | | |
| { _Silurian_ { Lower, or | Age of | |
| { { Siluro-Cambrian. | _Mollusks_, | (Earliest |
| { | _Corals_ and |Land Plants.) |
| { { Upper. |_Crustaceans_. |Age of _Algæ_.|
| { _Cambrian_ { Middle. | | |
| { { Lower. | | |
| | | |
+---------------------------------------+---------------+--------------+
| | | |
| EOZOIC. | | |
| { _Huronian_ { Upper. | | |
| { { Lower. | Age of | Indications |
| { | _Protozoa_. | of Plants |
| { { Upper, or Norian. | (First Animal | not |
| { _Laurentian_ { Middle, | Remains.) | determinable.|
| { { Lower, or Bojian. | | |
| | | |
+---------------------------------------+---------------+--------------+
In the oldest rocks known to geologists--those of the Eozoic
time--some indications of the presence of life are found. Great beds
of limestone are contained in these formations, vast quantities of
carbon in the form of graphite, and thick beds of iron-ore. All these
are known, from their mode of occurrence in later deposits, to be
results, direct or indirect, of the agency of life; and if they
afforded no traces of organic forms, still their chemical character
would convey a presumption of their organic origin. But additional
evidence has been obtained in the presence of certain remarkable
laminated forms penetrated by microscopic tubes and canals, and which
are supposed to be the remains of the calcareous skeletons of
humbly-organized animals akin to the simplest of those now living in
the sea. Such animals--little more than masses of living animal
jelly--now abound in the waters, and protect themselves by secreting
calcareous skeletons, often complex and beautiful, and penetrated by
pores, through which the soft animal within can send forth minute
thread-like extensions of its body, which serve instead of limbs. The
Laurentian fossil known as _Eozoon Canadense_ (see Fig. 3) may have
been the skeleton of such a lowly-organized animal; and if so, it is
the oldest living thing that we know. But if really the skeleton or
covering of such an animal, _Eozoon_ is larger than any of its
successors, and quite as complex as any of them. There is nothing to
show that it could have originated from dead matter by any
spontaneous action, any more than its modern representatives could do
so. There is no evidence of its progress by evolution into any higher
form, and the group of animals to which it belongs has continued to
inhabit the ocean throughout geological time without any perceptible
advance in rank or complexity of structure. If, then, we admit the
animal nature of this earliest fossil, we can derive from it no
evidence of monistic evolution; and if we deny its animal nature, we
are confronted with a still graver difficulty in the next succeeding
formations.
[Illustration: FIG. 3.
1. Small specimen of _Eozoon Canadense_, weathered out from
the containing rock, and showing its laminated structure.
2. Casts of irregular or acervaline chambers of upper part
(magnified).
3. Surface of a cast of a flat chamber, showing its
constituent chamberlets (magnified).
4. Section of casts of flat chambers (magnified). From the
Laurentian of Canada.]
Between the rocks which contain _Eozoon_ and the next in which we find
any abundant remains of life, there is a gap in geological history,
either destitute of evidence of life or showing nothing materially in
advance of _Eozoon_. In the Cambrian Age, however, we obtain a vast
and varied accession of life. Here we find evidence that the sea
swarmed with living creatures near akin to those which still inhabit
it, and nearly as varied. Referring merely to leading groups, we have
here the soft shellfishes and the worms, the ordinary shellfishes, the
sea-stars, and the corals, with the sponges. In short, had we been
able to drop our dredge into the Cambrian or Lower Silurian ocean, we
should have brought up representatives of all the leading types of
invertebrate life that exist in the modern seas--different, it is
true, in details of structure from those now existing, but constructed
on the same principles and filling the same places in nature.
If we inquire as to the history of this swarming marine life of the
early Palæozoic, we find that its several species, after enduring for
a longer or a shorter time, one by one became extinct and were
replaced by others belonging to the same groups. Thus there is in each
great group a succession of new forms, distinct as species, but not
perceptibly elevated in the scale of being. In many cases, indeed, the
reverse seems to be the case; for it is not unusual to find the
successive dynasties of life in any one family manifesting degradation
rather than elevation. New, and sometimes higher, forms, it is true,
appear in the progress of time, but it is impossible, except by
violent suppositions, to connect them genetically with any
predecessors. The succession throughout the Palæozoic presents the
appearance rather of the unchanged persistence of each group under a
succession of specific forms, and the introduction from time to time
of new groups, as if to replace others which were in process of decay
and disappearance.
In the later half of the Palæozoic we find a number of higher forms
breaking upon us with the same apparent suddenness as in the case of
the early Cambrian animals. Fishes appear, and soon abound in a great
variety of species, representing types of no mean rank, but,
singularly enough, belonging, in many cases, to groups now very rare;
while the commoner tribes of modern fish do not appear. On the land,
batrachian reptiles now abound, some of them very high in the
sub-class to which they belong. Scorpions, spiders, insects, and
millipedes appear, as well as land-snails, and this not in one
locality only, but over the whole northern hemisphere. At the same
time, the land appears clothed with an exuberant vegetation--not of
the lowest types nor of the highest, but of intermediate forms, such
as those of the pines, the club-mosses, and the ferns, all of which
attained in those days to magnitudes and numbers of species
unsurpassed, and in some cases unequalled, in the modern world. Nor do
they show any signs of an unformed or imperfect state. Their seeds
and spores, their fruits and spore-cases, are as elaborately
constructed, the tissues and forms of their stems and leaves as
delicate and beautiful, as in any modern plants. So with the compound
eyes and filmy wings of insects, the teeth, bones, and scales of
batrachians and fishes; all are as perfectly finished, and many quite
as complex and elegant, as in the animals of the present day (Figure
4).
[Illustration: FIG. 4.
Restoration (by _G. F. Matthew_) of a Trilobite
(_Paradoxides_) from the Lower Cambrian, as an evidence of the
existence of crustacean animals of high type and great
complexity in this early age. If such animals were evolved
from Protozoa by slow and gradual changes, the time required
would be greater than that which intervened between the
Cambrian period and the present time.]
This wonderful Palæozoic Age was, however, but a temporary state of
the earth. It passed away, and was replaced by the Mesozoic,
emphatically the reign of reptiles, when animals of that type attained
to colossal magnitude, to variety of function and structure, to
diversity of habitat in sea and on land, altogether unexampled in
their degraded descendants of modern times. Sea-lizards of gigantic
size swarmed everywhere in the waters. On land, huge quadrupeds, like
Atlantosaurus and Iguanodon and Megalosaurus, greatly exceeded the
elephants of later times; while winged reptiles--some of them of small
size, others with wings twenty feet in expanse--flitted in the air.
Strangely enough, with these reptilian lords appeared a few small and
lowly mammals, forerunners of the coming age. Birds also make their
appearance, and at the close of the period forests of broad-leaved
trees altogether different from those of the Palæozoic Age, and
resembling those of our modern woods, appear for the first time over
great portions of the northern hemisphere.
The Cainozoic, or Tertiary, is the age of mammals and of man. In it
the great reptilian tyrants of the Mesozoic disappear, and are
replaced on land and sea by mammals or beasts of the same orders with
those now living, though differing as to genera and species (see Fig.
5). So greatly, indeed, did mammalian life abound in this period that
in the middle part of the Tertiary most of the leading groups were
represented by more numerous species than at present; while many
groups then existing have now no representatives. At the close of this
great and wonderful procession of living beings comes man himself--the
last and crowning triumph of creation; the head, thus far, of life on
the earth.
I have merely glanced at the leading events of this wonderful history,
because its details may be found in so many manuals and popular works
on geology. But if we imagine this great chain of life extending over
periods of enormous duration in comparison with the short span of
human history, presenting to the naturalist hosts of strange forms
which he could scarcely have imagined in his dreams, we may understand
how exciting have been these discoveries crowded within the lives of
two generations of geologists. Further, when we consider that the
general course of this great development of life, beginning with
Protozoa and ending with man, is from below upward--from the more
simple to the more complex--and that there is of necessity, in this
grand growth of life through the ages, a likeness or parallelism to
the growth of the individual animal from its more simple to its more
complex state, we can understand how naturalists should fancy that
here they have been introduced to the workshop of Nature, and that
they can discover how one creature may have been developed from
another by spontaneous evolution.
[Illustration: FIG. 5.
Skeleton of the American Mastodon, illustrating the number and
wide distribution of elephantine animals of the three genera
_Dinotherium_, _Mastodon_, and _Elephas_ in the later Tertiary
Age. Gaudry, the most eminent modern authority on these
animals, remarks that the facts at present known do not
"permit us to indicate any relation of descent between the
elephantine animals and those of other orders known to us at
present."]
Many naturalists like Darwin and Haeckel, as well as philosophers like
Herbert Spencer, are quite carried away by this analogy, and appear
unable to perceive that it is merely a general resemblance between
processes altogether different in their nature, and therefore in
their causes. The greater part, however, of the more experienced
palæontologists, or students of fossils, have long ago seen that in
the larger field of the earth's history there is very much that cannot
be found in the narrower field of the development of the individual
animal; and they have endeavored to reduce the succession of life to
such general expressions as shall render it more comprehensible and
may at length enable us to arrive at explanations of its complex
phenomena. Of these general expressions or conclusions I may state a
few here, as apposite to our present subject, and as showing how
little of real support the facts of the earth's history give to the
pseudo-gnosis of monistic evolution.
1. The chain of life in geological time presents a wonderful testimony
to the reality of a beginning. Just as we know that any individual
animal must have had its birth, its infancy, its maturity, and will
reach an end of life, so we trace species and groups of species to
their beginning, watch their culmination, and perhaps follow them to
their extinction. It is true that there is a sense in which geology
shows "no sign of a beginning, no prospect of an end;" but this is
manifestly because it has reached only a little way back toward the
beginning of the earth as a whole, and can see in its present state no
indication of the time or manner of the end. But its revelation of the
fact that nearly all the animals and plants of the present day had a
very recent beginning in geological time, and its disclosure of the
disappearance of one form of life after another as we go back in time,
till we reach the comparatively few forms of life of the Lower
Cambrian, and finally have to rest over the solitary grandeur of
_Eozoon_, oblige it to say that nothing known to it is self-existent
and eternal.
2. The geological record informs us that the general laws of nature
have continued unchanged from the earliest periods to which it relates
until the present day. This is the true "uniformitarianism" of geology
which holds to the dominion of existing causes from the first. But it
does not refuse to admit variations in the intensity of these causes
from time to time, and cycles of activity and repose, like those that
we see on a small scale in the seasons, the occurrence of storms, or
the paroxysms of volcanoes. When we find that the eyes of the old
trilobites have had lenses and tubes similar to those in the eyes of
modern crustaceans, we have evidence of the persistence of the laws of
light. When we see the structures of Palæozoic leaves identical with
those of our modern forests, we know that the arrangements of the
soil, the atmosphere, and the rain were the same at that ancient time
as at present. Yet, with all this, we also find evidence that
long-continued periods of physical quiescence were followed by great
crumplings and foldings of the earth's crust, and we know that this
also is consistent with the operation of law; for it often happens
that causes long and quietly operating prepare for changes which may
be regarded as sudden and cataclysmic.
3. Throughout the geological history there is progress toward greater
complexity and higher grade, along with degradation and extinction.
Though experience shows that it may be quite possible that new
discoveries may enable us to trace some of the higher forms of life
farther back than we now find them, yet there can be no question that
in the progress of geological time lower types have given place to
higher, less specialized to more specialized. Curiously enough, no
evidence proves this more clearly than that which relates to the
degradation of old forms. When, for example, the reptiles of the
Mesozoic Age were the lords of creation, there was apparently no place
for the larger Mammalia which appear at the close of the reptile
dynasty. So in the Palæozoic, when trees of the cryptogamous type
predominated, there seems to have been no room in nature for the
forests of modern type which succeeded them. Thus the earth at every
period was fully peopled with living beings--at first with low and
generalized structures which attained their maxima at early stages and
then declined, and afterward with higher forms which took the places
of those that were passing away. These latter, again, though their
dominion was taken from them, were continued in lower positions under
the new dynasties. Thus none of the lower types of life introduced was
finally abandoned, but, after culminating in the highest forms of
which it was capable, each was still continued, though with fewer
species and a lower place. Examples of this abound in the history of
all the leading groups of animals and plants.
4. There is thus a continued plan and order in the history of life
which cannot be fortuitous. The chance interaction of organisms and
their environment, even if we assume the organisms and environment as
given to us, could never produce an orderly continuous progress of the
utmost complexity in its detail, and extending through an enormous
lapse of time. It has been well said that if a pair of dice were to
turn up aces a hundred times in succession, any reasonable spectator
would conclude that they were loaded dice; so if countless millions of
atoms and thousands of species, each including within itself most
complex arrangement of parts, turn up in geological time in perfectly
regular order and a continued gradation of progress, something more
than chance must be implied. It is to be observed here that every
species of animal or plant, of however low grade, consists of many
co-ordinated parts in a condition of the nicest equilibrium. Any
change occurring which produces unequal or disproportionate
development, as the experience of breeders of abnormal varieties of
animals and plants abundantly proves, imperils the continued existence
of the species. Changes must, therefore, in order to be profitable,
affect the parts of the organism simultaneously and symmetrically. The
chances of this may well be compared to the casting of aces a
hundred times in succession, and are so infinitely small as to be
incredible under any other supposition than that of intelligent
design.
[Illustration: FIG. 6.
Group of Plants (restored) from the Devonian period,
illustrating the complexity and beauty of the earliest known
land vegetation, though many of the leading forms of modern
plants are unknown in this very ancient period.]
5. The progress of life in geological time. Just as the growth of
trees is promoted or arrested by the vicissitudes of summer and
winter, so in the course of the geological history there have been
periods of pause and acceleration in the work of advancement. This is
in accordance with the general analogy of the operations of nature,
and is in no way at variance with the doctrine of uniformity already
referred to. Nor has it anything in common with the unfounded idea, at
one time entertained, of successive periods of entire destruction and
restoration of life. Prolific periods of this kind appear in the
marine invertebrates of the early Cambrian, the plants (Figure 6) and
fishes of the Devonian, the batrachians of the Carboniferous, the
reptiles of the Trias, the broad-leaved trees of the Cretaceous, and
the mammals of the early Tertiary. A remarkable contrast is afforded
by the later Tertiary and modern time, in which, with the exception of
man himself, and perhaps a very few other species, no new forms of
life have been introduced, while many old forms have perished. This
is somewhat unfortunate, since, in such a period of stagnation as that
in which we live, we can scarcely hope to witness either the creation
or the evolution of a new species. Evolutionists themselves--those, at
least, who are willing to allow their theory to be at all modified by
facts--now perceive this; and hence we have the doctrine, advanced by
Mivart, Le Conte, and others, of "critical periods," or periods of
rapid evolution alternating with others of greater quiescence. It is
further to be observed here that in a limited way and with reference
to certain forms of life we can see a reason for these intermittent
creations. The greater part of the marine fossils known to us are from
rocks now raised up in our continents, and they lived at periods when
the continents were submerged. Now, in geological time these periods
of submergence alternated with others of elevation; and it is manifest
that each period of continental submergence gave scope for the
introduction of numbers of new marine species, while each continental
elevation, on the other hand, gave opportunity for the increase of
land-life. Further, periods when a warm climate prevailed in the
arctic regions--periods when plants such as now live in temperate
regions could enjoy six months of continuous sunshine--were eminently
favorable to the development of such plants, and were utilized for the
introduction of new floras, which subsequently spread to the
southward. Thus we see physical changes occurring in an orderly
succession and made subservient to the progress of life.
6. There is no direct evidence that in the course of geological time
one species has been gradually or suddenly changed into another. Of
the latter we could scarcely expect to find any evidence in fossils;
but of the former, if it had occurred, we might expect to find
indications in the history of some of the numerous species which have
been traced through successive geological formations. Species which
thus continue for a great length of time usually present numerous
varietal forms which have sometimes been described as new species; but
when carefully scrutinized they are found to be merely local and
temporary, and to pass into each other. On the other hand, we
constantly find species replaced by others entirely new, and this
without any transition. The two classes of facts are essentially
different; and though it is possible to point out in the newer
geological formations some genera and species allied to others which
have preceded them, and to suppose that the later forms proceeded from
the earlier, still, when the connecting-links cannot be found, this is
mere supposition, not scientific certainty. Further, it proceeds on
the principle of arbitrary choice of certain forms out of many without
any evidence of genetic connection. The worthlessness of such
derivation is well shown in a case which has often been paraded as an
illustration of evolution--the supposed genealogy of the horse. In
America a series of horse-like animals has been selected, beginning
with the _Orohippus_ of the Eocene, and these have been marshalled as
the ancestors of the fossil horses of America; for there are no native
horses in America in the modern period. Yet this is purely arbitrary,
and dependent merely on a succession of genera more and more closely
resembling the modern horse being procurable from successive Tertiary
deposits, often widely separated in time and place. In Europe, on the
other hand, the ancestry of the horse has been traced back to
_Palæotherium_--an entirely different form--by just as likely
indications. Both genealogies can scarcely be true, and there is no
actual proof of either. The existing American horses, which are of
European parentage, are, according to the theory, descendants of
_Palæotherium_, not of _Orohippus_; but if we had not known this on
historical evidence, there would have been nothing to prevent us from
tracing them to the latter animal. This simple consideration alone is
sufficient to show that such genealogies are not of the nature of
scientific evidence.
It is further to be observed that some of the ablest palæontologists,
and those who have enjoyed the largest opportunities of observation
and comparison, attach no value whatever to theories of evolution as
accounting for the origin of species. One of these is Joachim
Barrande, the palæontologist of Bohemia, and the first authority in
Europe on the fossils of the older formations. Barrande, like some
other eminent palæontologists, has the misfortune to be an unbeliever
in the modern gospel of evolution, but he has certainly labored to
overcome his doubts with greater assiduity than even many of the
apostles of the new doctrine; and if he is not convinced, the
stubbornness of the facts he has had to deal with must bear the
blame. In connection with his great and classical work on the Silurian
fossils of Bohemia, it has been necessary for him to study the similar
remains of every other country; and he has used this immense mass of
material in preparing statistics of the population of the Palæozoic
world more perfect than any other naturalist has been able to produce.
In successive memoirs he has applied these statistical results to the
elucidation of the history of the oldest group of crustaceans--the
trilobites--and the highest group of the mollusks--the cephalopods. In
his latest memoir of this kind he takes up the brachiopods, or
lamp-shells, a group of bivalve shellfishes very ancient and very
abundantly represented in all the older formations of every part of
the world, and which thus affords the most ample material for tracing
its evolution, with the least possible difficulty in the nature of
"imperfection of the record."
Barrande, in the publication before us, discusses the brachiopods with
reference, first, to the variations observed within the limits of the
species, eliminating in this way mere synonyms and varieties mistaken
for species. He also arrives at various important conclusions with
reference to the origin of species and varietal forms, which apply to
the cephalopods and trilobites as well as to the brachiopods, and some
of which, as the writer has elsewhere shown, apply very generally to
fossil animals and plants. One of these is that different
contemporaneous species, living under the same conditions, exhibit
very different degrees of vitality and variability. Another is the
sudden appearance at certain horizons of a great number of species,
each manifesting its complete specific characters. With very rare
exceptions, also, varietal forms are contemporaneous with the normal
form of their specific type, and occur in the same localities. Only in
a very few cases do they survive it. This and the previous results, as
well as the fact that parallel changes go on in groups having no
direct reaction on each other, prove that variation is not a
progressive influence, and that specific distinctions are not
dependent on it, but on the "sovereign action of one and the same
creative cause," as Barrande expresses it. These conclusions, it may
be observed, are not arrived at by that "slap-dash" method of mere
assertion so often followed on the other side of these questions, but
by the most severe and painstaking induction, and with careful
elaboration of a few apparent exceptions and doubtful cases.
His second heading relates to the distribution in time of the genera
and species of brachiopods. This he illustrates with a series of
elaborate tables, accompanied by explanation. He then proceeds to
consider the animal population of each formation, in so far as
brachiopods, cephalopods, and trilobites are concerned, with reference
to the following questions: (1) How many species are continued from
the previous formation unchanged? (2) How many may be regarded as
modifications of previous species? (3) How many are migrants from
other regions where they have been known to exist previously? (4) How
many are absolutely new species? These questions are applied to each
of fourteen successive formations included in the Silurian of Bohemia.
The total number of species of brachiopods in these formations is six
hundred and forty, giving an average of 45.71 to each, and the results
of accurate study of each species in its characters, its varieties,
its geographical and geological range, are expressed in the following
short statement, which should somewhat astonish those gentlemen who
are so fond of asserting that derivation is "demonstrated" by
geological facts:
1. Species continued unchanged 28 per cent.
2. Species migrated from abroad 7 "
3. Species continued with modification 0 "
4. New species without known ancestors 65 "
-------------
100 per cent.
He shows that the same or very similar proportions hold with respect
to the cephalopods and trilobites, and, in fact, that the proportion
of species in the successive Silurian faunæ which can be attributed to
descent with modification is absolutely _nil_. He may well remark that
in the face of such facts the origin of species is not explained by
what he terms _les élans poétiques de l'imagination_.
The third part of Barrande's memoir, relating to the comparison of the
Silurian brachiopods of Bohemia with those of other countries, though
of great scientific interest, and important in extending the
conclusions of his previous chapters, does not so nearly concern our
present subject.
I have thought it well to direct attention to these memoirs of
Barrande, because they form a specimen of conscientious work with the
view of ascertaining if there is any basis in nature for the doctrine
of spontaneous evolution of species, and, I am sorry to say, a
striking contrast to the mixture of fact and fancy on this subject
which too often passes current for science in England, America, and
Germany. Barrande's studies are also well deserving the attention of
our younger men of science, as they have before them, more especially
in the widely-spread Palæozoic formations of America, an admirable
field for similar work. In an appendix to his first chapter Barrande
mentions that the three men who in their respective countries are the
highest authorities on Palæozoic brachiopods, Hall, Davidson, and De
Koninck, agree with him in the main in his conclusions, and he refers
to an able memoir by D'Archiac in the same sense, on the cretaceous
brachiopods.
It should be especially satisfactory to those naturalists who, like
the writer, had failed to see in the palæontological record any good
evidence for the production of species by those simple and ready
methods in vogue with most evolutionists, to note the extension of
actual facts with respect to the geological dates and precise
conditions of the introduction of new forms, and to find that these
are more and more tending to prove the existence of highly complex
creative laws in connection with the great plan of the Creator as
carried out in geological time. These new facts should also warn the
ordinary reader of the danger of receiving without due caution those
general and often boastful assertions respecting these great and
intricate questions made by persons not acquainted with their actual
difficulty, or by enthusiastic speculators disposed to overlook
everything not in accordance with their preconceived ideas.
It may be asked, Is there, then, no place in the geological record
even for theistic evolution? This it would be rash to affirm. We can
only say that up to this time there is no proof of it. If nature has
followed this method, she seems carefully to have concealed the
process. If such changes have occurred as to evolve from a species,
say of mollusk or coral, belonging to one geological period some form
found in another period, and recognized as a distinct species, we have
to suppose that the capacity for such change was in some way implanted
in the species on its creation, and ready to be developed under
favorable conditions or in the lapse of time. For example, we may
suppose that a plant originating in the long arctic summers of a warm
period might, on migrating southward into the alternations of day and
night, undergo material changes. A marine animal long confined to a
limited sea-basin might, on being permitted to expand over a wide
submerged continent, be greatly modified in its structure and habits.
Up to a certain point we know that such changes have occurred, and
Barrande himself has largely illustrated them. As an example which I
have myself studied, I may refer to the common shells known on our
coasts as sand-clams (_Mya truncata and Mya arenaria_). The former
species, in the cold waters of the Glacial Age, assumed a short form
which it still retains in the arctic regions, and occasionally in the
colder waters of the more temperate regions, though there a more
elongated form prevails. Evidently the two forms are interchangeable
according to the temperature of the water. Still, if we could imagine
a permanent refrigeration over all the area occupied by the animal,
the short form only might survive, and might be supposed to be a
distinct species. This did not occur, however, even in the Glacial
Age, and is not likely to occur. Further, the allied, though quite
distinct, species _Mya arenaria_ has lived with the other through all
the long duration of the Post-Pliocene and modern periods, and, though
having its own range of varietal forms, has preserved its
distinctness. Cases of this kind are obviously of the nature of
varietal, not specific, change.
In conclusion, the whole of the facts and laws above detailed point to
a predetermined plan and to an intelligent Creator, of whose laws and
modes of procedure we may learn much by patient and careful study.
This surely gives a great additional interest to that marvellous story
of the earth which in these last days has been revealed to us by the
study of the rocks. We may also infer that not one method only but
many have been employed in replenishing the earth at first with living
beings, and in adding to these from time to time. To what extent we
may be able to understand these, time and future discoveries will
show. In the mean time, we can only suggest such general theories as
those referred to in the first of these lectures, but can affirm that
Agnostic Evolution is altogether abortive in its attempts to solve the
problem of the chain of life in geological time.