conclusions as to the climate of the period in which they lived, yet it
is only in the case of marine fossils, which constitute the majority
of such remains, that we acquire such knowledge, but it is mostly the
temperature of the sea which can thus be determined. However, let
it be remembered that, owing to the existence of heated currents,
the marine climate of a designated area does not necessarily imply a
correspondingly warm climate in the adjoining land, for land-climates
can only be determined by the relics of land-animals or land-plants,
and these are comparatively rare as fossils. But all conclusions on
this head are really based upon the existing distribution of vegetable
and animal life upon the globe, and are therefore liable to be vitiated
by the considerations that no certainty exists that the habits and
requirements of an extinct animal were exactly similar to those of its
nearest living relative; that far back in time groups of organisms, so
unlike anything we know at the present day, are met with, which render
all conjectures of climate based upon their supposed habits more or
less uncertain and unsafe; that in the case of marine animals we are
as yet very far from knowing the precise limits of distribution of
many species within our present seas as to render conclusions drawn
from living forms in relation to extinct species unsatisfactory and,
probably, incorrect; and, finally, that the distribution of animals
to-day, is certainly dependent on other conditions than climate alone,
the causes limiting the range of given animals being assuredly such as
belong to the existing order of things, and are different from what
they were in former times, not necessarily because the climate has
changed, but because of the alteration of other conditions that are
essential to the life of the species or conducive to its extension. But
notwithstanding the difficulties in the way, we are able in many cases
to deduce completely trustworthy conclusions concerning the climate
of a given geological period by an examination of its fossil remains.
In Eocene times, or at the beginning of the Tertiary Period, the
climate of what is now Western Europe was of a tropical or sub-tropical
character, the Eocene beds being found to contain the remains of
cowries and volutes, such shells as now inhabit tropical seas, together
with the fruits of palms and remains of other tropical plants. And
further, it has been shown that in Miocene times, or about the middle
of the same epoch, the central parts of Europe were peopled with a
luxuriant flora resembling that of the warmer parts of the United
States, and that Greenland, now buried for the most part beneath a vast
ice-shroud, was warm enough to support a large number of trees, shrubs
and other plants that are at present denizens of the temperate regions
of the globe.
And lastly, from the study of fossils, geologists first learned to
comprehend a fact, that is, that the crust of the earth is liable to
local elevations and subsidences, which may be regarded as of cardinal
importance in all modern geological theories and speculations. Long
after the remains of shells and those of other marine animals were
first observed in the solid rocks constituting the dry land, and at
great elevations above the sea-level, attempts were made to explain
this unintelligible phenomenon upon the hypothesis that these remains
or fossils were mere _lusus naturæ_, due to some “plastic virtue latent
in the earth.” But the common-sense of science soon rejected this idea,
and it was universally agreed that these bodies were really the relics
of animals that once lived in the sea. When once this was admitted,
further steps in the right way of thinking became comparatively easy,
and at the present day no geological doctrine stands on a surer
foundation than that which teaches that our existing continents and
islands, fixed and immovable as they appear, have been repeatedly sunk
beneath the ocean and just as repeatedly been lifted above its waters.
Not only have fossils an important bearing upon geology and
physiography as has been seen, but they have relations, most
complicated and weighty in character, with the science of biology, or
the study of living beings. No adequate understanding of zoölogy and
botany is possible without some acquaintance with the types of plants
and animals that have passed away, for there are numerous speculative
problems in the domain of vital science, which, if soluble at all,
can only hope to find their key in researches carried out on extinct
organisms.
No attempt will be made by the writer to discuss fully the biological
relations of fossils. Such an undertaking would afford matter for a
separate volume. All that I purpose in this chapter is to indicate very
cursorily the principal points of palæontological teaching, so that my
readers can acquire some idea of the progression from lower to higher
types that life has made throughout the geological ages. Preliminary to
the purpose held in view, let it be understood that the vast majority
of fossil animals and plants are extinct, or, differently and perhaps
more intelligently expressed, belong to species that no longer exist.
So far from there being any truth in the old idea that there have
been periodic destructions of all the living beings in existence upon
the earth, followed by a corresponding number of new creations of
plants and animals, the actual facts indicate that the extinction of
old and introduction of new forms have been processes that have been
continually going on throughout the whole of geologic time. Every
species seems to come into existence at a definite point of time, and
to disappear finally at another definite period, though there are few,
if any, instances, in which the times of entrance and exit could be
fixed with any degree of certainty or precision. Marked differences
in the actual time during which different species have remained in
existence are noticeable, and therefore corresponding differences in
their vertical range, or in the actual amount and thickness of strata
through which they present themselves as fossils, some species being
found to extend through two or three formations, and even a few have
had a more prolonged existence. More commonly, however, the species
which begin in the commencement of a great formation die out at or
before its close, while those which are introduced for the first time
near its middle or end may either become extinct or pass into the next
succeeding formation, animals of the lowest and simplest organization
as a rule having the longest range in time. Microscopic or minute
dimensions seem to favor longevity, for some of the Foraminifera
appear to have survived, with little or no perceptible alteration,
from the Silurian Period to the present day, whereas largely and
highly-organized animals, though long-lived as individuals, rarely seem
to live long specifically, and consequently have a restricted vertical
range. Exceptions to this rule are, however, occasionally found in some
persistent types, the Lampshells of the genus Lingula being little
changed from the Lingulæ that swarmed in the Lower Silurian seas, while
the existing Pearly Nautilus is the last descendant of a clan nearly as
old. Some forms, on the other hand, the Ammonites, which are closely
related to the Nautilus, and mostly restricted to certain zones of
strata, seem to have enjoyed a comparatively brief lease of life.
[Illustration: LIFE IN THE PRIMORDIAL SEA.
Representing Mollusks, Sponges, Crustaceans, Worms and Sea-Weeds.]
But of the causes that have led to the extinction of plants and
animals, little or nothing is known. All that can be affirmed, in our
present knowledge, is that the attributes constituting a species do
not seem to be intrinsically endowed with permanence, any more than
those constituting an individual, though the former may endure whilst
many successive generations of the latter have disappeared from the
earth. Each species, it would seem, has its own life-period--its
beginning, culmination and decay--the life-periods of different species
being of very different duration. From all that has been said, it
may be gathered that our existing plants and animals are for the
most part of modern origin, using the term modern in its geological
acceptation. Measured by human standards, many of our existing
animals, those which are capable of being preserved as fossils, are
known to have a high antiquity. Not a few of our shell-fish commenced
their existence at some time in the Tertiary, while one species of
Lampshell--_Terebratulina caput-serpentis_--is believed to have
survived since the Chalk, and a number of the Foraminifera date
from the Carboniferous Period. Thus, we learn the additional fact
that our existing flora and fauna do not constitute an aggregation
of organic forms which were introduced into the world collectively
and simultaneously, but that they commenced their existence at very
different times, some being extremely ancient, whilst others are of
comparatively recent origin. And this introduction of existing plants
and animals, as admirably shown by the study of the fossil shells of
the Tertiary Period, was a slow and gradual process. Ninety-five
per cent. of the known fossil shells in the earliest Tertiary are
found to be species no longer in existence, the remaining 5 per
cent. being forms that are known to live in our present seas. In the
Middle Tertiary, the extinct types are much fewer in number, while at
the close of the Period the proportion with which we started may be
reversed, not more than 5 per cent. being extinct types.
[Illustration: CARBONIFEROUS TIMES.
Animals and Plants That Prevailed.]
All existing animals belong to some five or six primary divisions,
which are technically known as sub-kingdoms, each sub-kingdom to be
regarded as representing a certain plan of structure, each and every
animal embraced therein being merely a modified form of this common
type. Not only are all known living animals reducible to these five or
six fundamental plans, but also the vast series of fossil forms which
have come to light in investigations of the earth’s strata. While many
fossil groups have no closely-related group now in existence, but in
no case do we meet with a fossil animal whose peculiarities do not
entitle it to be placed in one or other of the grand structural types
already indicated. The old types differ in many respects from those now
upon the earth, and the further we go back in time the more pronounced
does the divergence become. A comparison of the animals that lived
in the old Silurian seas with those now occupying our oceans, would
indicate differences so great in many instances as almost to place us
in another world, this divergence being most marked in the Palæozoic
forms of life, less so in those of the Mesozoic, and still less so in
the Tertiary. Each successive formation has therefore presented us with
animals becoming gradually more and more like those now in existence.
Though there is, however, an immense and striking difference between
the Silurian animals and those of the present day, yet this difference
is considerably lessened when a comparison is instituted between the
Silurian and the Devonian, and this with the Carboniferous, and so on
down to the present period.
Thus it follows that the animals of any given formation, and the plants
as well, where the records are preserved, are more like those of the
next formation below and of the next formation above, than they are
like any others. This fact of itself is an inexplicable one. But if
we believe that the animals and plants of any given formation are, in
part at any rate, the lineal descendants of those of the preceding,
and the progenitors, also in part at least, of those of the succeeding
formation, then the fact is readily comprehensible. So frequently
confronted is the palæontologist with the phenomenon of closely-related
forms, especially of animals, succeeding one another in point of time,
that he is compelled to believe that such forms have been developed
from some common ancestral type by some process of evolution. Upon
no other theory can we comprehend why the Post-Tertiary mammals of
South America should consist of edentates, llamas, tapirs, peccaries,
platyrhine monkeys and other forms now characterizing this continent,
while those of Australia should be exclusively referable to the
order of marsupials; and on no other view can we explain the common
occurrence of transitional forms of life, filling in the gaps between
groups now widely distinct. But, on the other hand, there are facts
which point clearly to the presence of some other law than that of
evolution, and probably of a deeper and more far-reaching character.
No theory of evolution can offer a satisfactory explanation for the
constant introduction throughout geological time of new forms of life,
which do not appear to be preceded by pre-existent allied types. The
graptolites and trilobites have no known predecessors, and leave no
known successors. Insects appear suddenly in the Devonian, and spiders
and myriopods in the Carboniferous, but all under well-differentiated
and highly-specialized forms. With equal apparent suddenness the
Dibranchiate Cephalopods show themselves in the older Mesozoic
deposits, and no known type of the Palæozoic period can be pointed to
as a possible ancestor. And so does the wonderful dicotyledonous flora
of the Upper Cretaceous similarly surprise us without any prophetic
annunciation from the older Jurassic. Many other instances might
be cited, but enough has been said to show that the problem is one
environed with profound difficulties.
[Illustration: MESOZOIC FLORA AND FAUNA.
Cycads, Pandanus, Deinosaurs, Birds and Pterodactyl.]
As we pass from the older rocks into the newer, we not only find that
the animals of each successive formation become gradually more and
more like existing species upon the globe, but we also find that there
has been a gradual progression and development in the types of animal
life which characterize the geological ages. Taking the earliest-known
and oldest examples of any given group, it can sometimes be shown
that these primitive forms, even though they are highly organized
themselves, possessed certain characters such as are now only to be met
with in the young of their existing representatives. Such characters,
which are technically called embryonic characters, do not prevent the
frequent attainment by their possessors of sizes much more gigantic
than those of their nearest living relatives. Moreover, these ancient
forms of life represent what are called comprehensive types, or types
that possess characters in combination such as are nowadays found
separately developed in different groups of animals. Such permanent
retention of embryonic characters and comprehensiveness of structural
type are signs of what zoölogists consider to be comparatively low
grades of organization, and their prevalence in the earlier forms of
animals is a very astonishing phenomenon, though they are none the less
perfectly organized so far as their peculiar type is concerned. As we
ascend the geological scale, these features will be found to gradually
disappear, higher and even higher forms will be introduced, and
specialization of type take the place of the former comprehensiveness.
That there has been in the past a general progression of organic
types, and that the appearance of the lower forms of life has in
the main preceded that of the higher forms in point of time, is a
widely-accepted generalization of palæontology.
Now that it has been seen that there has been a gradual progression
and development of animal types all through the ages up to the era of
man, the question naturally occurs whether or not the changes are still
going on which will result in a higher development. Man coexisted in
Western Europe with several remarkable mammals in the later portion
of the Post-Pliocene Period. While we do not know the causes which
led to the extinction of the mammoth, woolly rhinoceros, cave-lion
and others, yet we do know that scarcely any mammalian species have
become extinct during the historical period. The species with which man
coexisted are such that presumably required a very different climate to
that now prevailing in Western Europe. Some of the deposits in which
man’s remains have been found in association with the bones of extinct
mammals incontestably show that great changes in the physiography
and surface-configuration of the country had taken place since the
period of their accumulation, the human implements themselves bearing
evidence of an exceedingly barbarous condition of the human species.
Post-Pliocene, or Palæolithic man, was clearly unacquainted with the
use of the metals. Not only was this the case, but the workmanship of
these ancient races was much inferior to that of the later tribes,
who were also ignorant of the metals, and who also used nothing but
weapons and tools of stone, bone, etc., in war, chase and domestic
affairs. When first man spread over the earth, he had no domestic
animals, perhaps not even the dog, and had no knowledge of agriculture.
His weapons were of the rudest character, and his houses scarcely
worthy of the name. No doubt can exist that his food, habits and
entire manner of living have varied as he has passed from country to
country, for he must then have been far more subject to the influence
of external circumstances, and in all probability more susceptible of
change. Moreover, his form, which is now stereotyped by long ages of
repetition, may reasonably be presumed to have been more plastic than
is now the case. As long as man led a mere animal existence, he would
be subject to the same laws, and would vary in the same manner as the
rest of his fellow-creatures. But when at last he had acquired the
capacity of clothing himself, and of making weapons or tools, he has
taken away from nature, in a great measure, that power of changing the
external form and structure which she exercises over all other animals.
From the time, then, when his social and sympathetic feelings came
into active operation, and his intellectual and moral faculties became
fairly developed, man’s physical form and structure would not be so
much influenced by natural laws, and, therefore, as an animal, he would
become almost stationary, his environment ceasing to have upon him that
powerful modifying effect which it exercises over other parts of the
organic world. But from the moment that his body became less subject
to the changes of the surrounding universe, his mind would become
acted upon by the influences which the body had escaped. Every slight
variation in his mental and moral nature, which would consequently
be brought about, and which would enable him better to guard against
adverse circumstances, and league together for mutual comfort and
protection, would be preserved and accumulated. The better and higher
specimens of our race would therefore increase and diffuse themselves,
while the lower and more brutal would succumb and successively die out,
and that rapid advancement of mental organization would occur, which
has raised the very lowest races of men, whose mentality was scarcely
superior to the animal, to that high position which it has attained in
the Germanic races. It would be too bold an assertion to say that man’s
body has become stationary. Slow and gradual changes still take place,
although his mere bodily structure long ago became of less importance
to him than that subtle energy, which is termed mind. No one can doubt
that _this_ gave his naked and unprotected body clothing against the
varying inclemencies of the seasons and enabled him to compete with the
deer in swiftness and the wild bull in strength by giving him weapons
wherewith to capture or subdue them both. Though less capable than most
other animals of subsisting on the herbs and the fruits of unaided
nature, it was this wonderful faculty that taught him to govern and
direct nature to his own benefit, and compel her to produce food for
him when and where he pleased. From the moment, then, when the first
skin was used as a covering, the first rude spear fashioned to aid in
the chase, and the first seed sown or shoot planted, a grand revolution
was effected in nature, a revolution which had had no parallel in all
the previous cycles of the world’s history, for a being had arisen
who was no longer necessarily subject to a changing universe, a being
who was in some degree superior to nature, inasmuch as he knew how to
control and regulate her action, and could maintain himself in unison
with her, not by a change brought about in the body, but by a growth
and advance in mind. Therein are shadowed forth the true grandeur and
dignity of man. Not only has he achieved for himself a great victory
in this rising by the power of mind superior to nature in a sense, but
he has also gained a directing influence over other existences, in
that he has been able to grasp from nature some of that power which,
before his appearance, she universally exercised. From all that man has
accomplished in the past, it is easy to anticipate the time when only
cultivated plants and domestic animals will be produced by the earth,
and when the ocean, which, for countless cycles of ages ruled supreme
over the globe, will be the only domain in which that power can be
exercised.