laws which regulate the formation of crystals. The chemist finds that the
same substance, when it crystallizes, invariably takes the same
geometrical forms. The nucleus or primary form, with a few exceptions, of
no importance in the present argument, to which all these secondary forms
may be reduced by change, is one particular solid, with unvarying angles;
and all the secondary forms, built upon the primary, correspond in their
angles. In short, in crystallography we have another example of perfect
practical mathematics, as perfect as the theory.
Now, the oldest rocks in the globe contain crystals, and so do the rocks
of all ages, sometimes of the same kind as those produced in the chemist's
laboratory. And they are found to correspond precisely. It matters not
whether they were the produce of nature's laboratory countless ages ago,
or of the skill of the nineteenth century,--the same mathematics ruled in
their formation with a precision which infinite wisdom alone could secure.
_In the second place, the laws of meteorology have ever been the same as
at present._
Under meteorological laws I include all atmospheric phenomena. And
although we have no direct proof from geology in respect to the more rare
of these phenomena, such as the aurora borealis and australis, and
transient meteors, yet in respect to the existence of clouds, wind, and
rain, the evidence is quite striking. In several places in Europe, and in
many in this country, are found, upon layers of the new red sandstone, the
distinct impressions of rain drops, made when the rock was fine mud. They
correspond precisely with the indentations which falling rain-drops now
make upon mud, and they show us that the phenomena of clouds and storms
existed in that remote period, and that the vapor was condensed as at
present. In the fact that the animals entombed in the rocks of various
ages are found to have had organs of respiration, we also infer the
existence of an atmosphere analogous to that which we now breathe. The
rain-drops enable us to proceed one step farther; for often they are
elongated in one direction, showing that they struck the ground obliquely,
doubtless in consequence of wind. In short, the facts stated enable us to
infer, with strong probability, that atmospheric phenomena were then
essentially the same as at present; and analogy leads us to a similar
conclusion as to all the past periods of the world's history, certainly
since animals were placed upon it. What a curious register do these
rain-drops present us! an engraving on stone of a shower that fell
thousands and thousands of ages ago! They often become, too, an
anemoscope, pointing out the direction of the wind, while the petrified
surface shows us just how many drops fell, quite as accurately as the most
delicate pluviameter. What events in the earth's pre-Adamic history would
seem less likely to come down to us than the pattering of a shower?
_In the third place, the agents of geological change appear to have been
always the same on the earth._
Whoever goes into a careful examination of the rocks will soon become
satisfied that no fragment of them all remains in the condition in which
it was originally created. Whatever was the original form in which matter
was produced, there is no longer any example of it to be found. The
evidence of these changes is as strong almost as that constant changes are
going on in human society. And we find them constantly progressing among
the rocks, as well as among men; nor do the agents by which they are
produced appear to have been ever different from those now in operation.
The two most important are heat and water; and it is doubtful whether
there is a single particle of the globe which has not experienced the
metamorphic action of the one or the other. Indeed, it is nearly certain
that every portion of the globe has been melted, if not volatilized. All
the unstratified rocks have certainly been fused, and probably all the
stratified rocks originated from the unstratified, and have been modified
by water and heat. In many of these rocks, especially the oldest, we
perceive evidence of the joint action of both these agents. Evidently they
were once aqueous deposits; but they appear to have been subsequently
subjected to powerful heat. As we ascend on the scale of the stratified
rocks, the marks of fire diminish, and those of water multiply, so that
the latest are mere mechanical or chemical depositions from water.
In these facts, then, we see proof that heat and water have been the chief
agents of geological change since the first formation of a solid crust on
the globe; for some of the rocks now accessible, as already stated, date
their origin at that early period. We might also trace back the agency of
heat much farther, if the hypothesis adopted by not a few eminent
geologists be true, which supposes the earth to have been once in a
gaseous state from intense heat. But to press this point will add very
little to my argument, even could I sustain it by plausible reasoning. I
will only say, that, so far as we know any thing of the state of the earth
previous to the consolidation of its crust, heat appears to have been the
chief agent concerned in its geological changes.
Among other agencies of less importance, that have always operated
geologically, is gravity. Its chief effect, at present is to bring the
earth's surface nearer and nearer to a level, by causing the materials,
which other agencies have loosened from its salient parts, to subside into
its cavities and valleys. It also condenses many substances from a gaseous
to a liquid or solid state, especially those deep in the earth's crust,
and thus brings the particles more within the reach of cohesive
attraction and chemical affinity, often changing the constitution, and
always the solidity, of bodies. And in the position of the ancient
mechanical rocks, occupying as they do the former basins of the surface,
and in the superior consolidation of the earlier strata, we find proof of
the action of gravity in all past geological time.
Electricity too, in the form of galvanism, has never been idle. We have
reason to think that it operates at this moment in accumulating metallic
ores in veins; and this segregation appears to have operated in all ages,
not only in filling veins, but also, probably, in giving a laminated
character and jointed structure to mountains of slate, as well as a
concretionary and prismatic form to others.
Last, though not least, we may reckon among the agents of geological
change the forces of cohesion and affinity. When water and heat, gravity
and galvanism, have brought the atoms of bodies into a proper state, these
agents are always ready to change their form and constitution; and they
have ever been at hand to operate by the same laws, and we witness their
effects in the oldest as well as the newest rocks found in the earth's
crust. This point, however, has been sufficiently considered, when
treating of the unvarying uniformity of the laws of chemistry and
crystallography.
But though the nature of the agencies above considered has never changed,
the intensity or amount of their action has varied; how much is a point
not yet settled among geologists. Some regard that intensity, as it has
existed during the present or alluvial period, as a standard for all
preceding periods; that is, the intensity of these forces has never varied
more during any period of the earth's history than it has since the
alluvial period commenced. Most geologists, however, regard this as an
extreme opinion, and think they see evidence in geology of a far greater
intensity in these agencies in past periods than exists at present. They
think they have proof that the world was once only a molten mass of
matter, and some evidence that previously it was in a state of vapor. They
believe that vast mountains, and even continents, have sometimes been
thrown up from the ocean's bed by a single mighty paroxysmal effort; and
such effects they know to be far greater than the causes of change now in
operation can produce, without a vast increase of their intensity. But
this question need neither be discussed nor decided for the sake of my
present argument, since my object is to prove an identity in the nature
and laws, not in the intensity, of geological agencies.
_In the fourth place, the laws of zoology and botany have always been the
same on the globe._
An examination of the animals now living, amounting to some hundred
thousand species, perhaps to one or two millions, shows that they may be
arranged in four great classes. The first class embraces the vertebral
animals, distinguished by having a vertebral column, or back-bone, a
regular skeleton, and a regular nervous system. It comprehends all the
quadrupeds and bipeds, with man at their head, and is much superior to all
other classes in complexity of organization and strength of the mental
powers. The second class embraces the mollusks, or animals inhabiting
shells. They are destitute of a spinal marrow, and for the most part their
muscles are attached to the external covering, called the shell, although
this shell is sometimes internal. The third class are called articulated
animals, having envelopes connected by annulated plates, or rings. It
includes such animals as the lobster, bloodsucker, spider, and insects
generally. The fourth class have a radiated structure, and often resemble
plants, or their habitation is a stony structure. Hence they are sometimes
called zoophytes, which means _animal plants_; or lithophytes, which means
_stony plants_. They swarm in the ocean, and some of them build up those
extensive stony structures called coral reefs.
Now, if we examine the descriptions of the organic remains in the rocks,
we find that in all ages of the world these four great classes of animals
have existed. But in the earliest times, the three last classes--the
mollusks, the articulated, and the radiated tribes--vastly preponderated,
while the vertebral class had only a few representatives; and it is not
till we rise as high as the new red sandstone, that we meet with any,
except fishes, save a few batrachians in the old red sandstone, and the
carboniferous group, detected alone by their tracks. Then the reptiles
began to appear in abundance, with tortoises and enormous birds of a low
organization, but no mammiferous animal is found, until we reach the
oolite; and scarcely any till we rise to the tertiary strata, when they
became abundant; but not so numerous as at present, though for the most
part of larger size. Thus we find that the more perfect animals have been
developed gradually, becoming more and more complex as we rise on the
scale of the rocks. But in the three other classes, there does not appear
to have been much advance upon the original types, although in numbers and
variety there has been a great increase.
The plants now growing upon the globe, amounting probably to nearly one
hundred thousand species, are divided into two great classes, by a very
decided character. Some of them have distinct flowers, and others are
destitute of them. The former are called phenogamian, or flowering plants;
and the latter cryptogamian, or flowerless plants.
At present, the flowering plants very much predominate in the flora of
every country. But in the earliest periods of organic existence, the
reverse was the case. We find, indeed but very few flowering plants, and
these of a character somewhat intermediate between flowering and
flowerless; such as the coniferae and cycadeae, including the pine tribe. A
few palms appeared almost as early, and some other monocotyledons. But
most of the dicotyledons did not appear till the tertiary period, where
more than two hundred species have been found. Of the three hundred
species found in and beneath the carboniferous group, two thirds are tree
ferns, or gigantic equisetaceae. More than one third of the entire flora of
the secondary formation consists of cycadeae; whereas, this family of
plants forms not more than the two thousandth part of the existing flora.
In short, we find the more perfect plants as well as animals to be few in
the earliest periods, and to have been gradually introduced up to the
present time. But as to the flowerless plants, most of them seem to have
been as perfect at first as they now are.
These facts teach us conclusively that the outlines of organic life on the
globe have always been the same; that the great classes of animals and
plants have always had their representatives, and that the variations
which have been introduced, have been merely adaptations to the varying
condition of the earth's surface. The higher and more complex natures,
both of animals and plants, were not introduced at first, because the
surface was not adapted to their existence; and they were brought in only
as circumstances, favorable to their development, prepared the way.
There is another fact of great interest on this subject. Even a cursory
examination of the animals and plants now on the globe, shows such a
gradation of their characters that they form a sort of chain, extending
from the most to the least perfect species. But we see at once that the
links of this chain are of very unequal length; or, rather, that there are
in some instances wide intervals between the nearest species, as if one or
more links had dropped out. How remarkable that some of these lost links
should be found among the fossil species! I will refer to a few examples.
Among existing animals no genera or tribes are more widely separated than
those with thick skins, denominated pachydermata; such as the rhinoceros
and the elephant. But among the fossil animals of the tertiary strata,
this tribe of animals was much more common; and many of them fill up the
blanks in the existing families, and thus render more perfect and uniform
the great chain of being which binds together into one great system the
present and past periods of organic life.
A similar case occurs among fossil plants. In tropical climates we find a
few species--not much over twenty--of a singular family of plants, the
cycadeae connecting the great families of coniferae, or dicotyledons, with
the palms, which are monocotyledonous, and the ferns, which are
acotyledonous. The chasm, however, between those great and dissimilar
classes of plants is but imperfectly filled by the few living species of
cycadeae. But of the fossil species hitherto found above the coal
formation, almost one half are cycadeae; so that here, too, the lost links
of the chain are supplied.
"Facts like these," says Dr. Buckland, "are inestimably precious to the
natural theologian, for they identify, as it were, the Artificer, by
details of manipulation throughout his works. They appeal to the
physiologist, in language more commanding than human eloquence; the voice
of very stocks and stones, that have been buried for countless ages in the
deep recesses of the earth, proclaiming the universal agency of one
all-directing, all-sustaining Creator, in whose will and power these
harmonious systems originated, and by whose universal providence they are,
and have at all times been, maintained."--_Bridgewater Treatise_, vol. i.
p. 502.
One other fact, showing the identity of former zoological laws with those
which now prevail, must not be omitted. I refer to the existence on the
globe in all past periods of organic life of the two great classes of
carnivorous and herbivorous animals; and they have always existed, too, in
about the same proportion. To the harmony and happiness of the present
system, we know that the existence and proper relative number of these
different classes are indispensable. For in order that the greatest
possible number of animals that live on vegetable food should exist, they
must possess the power of rapid multiplication, so that there should be
born a much larger number than is necessary to people the earth. But if
there existed no carnivorous races to keep in check this redundancy of
population, the world would soon become so filled with the herbivorous
races that famine would be the consequence, and thus a much greater amount
of suffering result than the sudden death inflicted by carnivorous races
now produces. To preserve, then, a proper balance between the different
species is, doubtless, the object of the creation of the carnivorous. This
system has been aptly denominated "the police of nature." And we find it
to have always existed. The earliest vertebral animals--the sauroid fishes
and sharks--were of this description. The sharks have always lived, but
the sauroid fishes became less numerous when other marine saurians were
created; and when they both nearly disappeared, during the tertiary
period, other predaceous families were introduced, more like those now in
existence.
The history of the mollusks, or animals inhabiting shells, furnishes us
with an example still more striking. These animals, as they now exist, are
divisible into the two great classes of carnivorous and herbivorous
species, being distinguished by their anatomical structure; and so has it
ever been. In the fossiliferous rocks below the tertiary, we find immense
numbers of nautili, ammonites, and other kindred genera of polythalamous
shells, called cephalopods, which were all carnivorous. And when they
nearly disappeared with the cretaceous period, there was created another
race with carnivorous propensities and organs, called trachelipods; and
those continue still to swarm in the ocean. Had they not appeared when the
cephalopods passed away, the herbivorous tribes would have multiplied to
such an extent as ultimately to destroy marine vegetation, and bring on
famine among themselves.
These examples are sufficient to prove the existence of the carnivorous
and herbivorous races in all ages and in about the same relative numbers.
And it certainly furnishes most decisive evidence of the oneness of all
these systems of organic life on the globe.
_In the fifth place, the laws of anatomy have always been the same since
organic structures began to exist._
It had long been known that the organs of animals were beautifully adapted
to perform the functions for which they were intended. But it was not till
the investigations of Baron Cuvier, within the last half century, that it
was known how mathematically exact is the relation between the different
parts of the animal frame, nor how precise are the laws of variation in
the different species, by which they are fitted to different elements,
climates, and food. It is now well known, that each animal structure
contains a perfect system of correlation, and yet the whole forms a
harmonious part of the entire animal system on the globe. But the
language of Cuvier himself will best elucidate this subject, so far as it
is capable of popular explanation.
"Every organized individual," says he, "forms an entire system of its own;
all the parts of which mutually correspond, and concur to produce a
certain definite purpose, by reciprocal reaction, or by combining towards
the same end. Hence none of these separate parts can change their forms
without a corresponding change in the other parts of the same animal, and
consequently each of these parts, taken separately, indicates all the
other parts to which it has belonged. Thus, if the viscera of any animal
are so organized as only to be fitted for the digestion of recent flesh,
it is also requisite that the jaws should be so constructed as to fit them
for devouring prey; the claws must be constructed for seizing and tearing
it to pieces; the teeth for cutting and dividing its flesh; the entire
system of the limbs, or organs of motion, for pursuing and overtaking it;
and the organs of sense, for discovering it at a distance. Nature, also,
must have endowed the brain of the animal with instinct sufficient for
concealing itself, and for laying plans to catch its necessary victims.
"In order that the jaw may be well adapted for laying hold of objects, it
is necessary that its condyle should have a certain form; that the
resistance, the moving power, and the fulcrum, should have a certain
relative position with respect to each other, and that the temporal
muscles should be of a certain size; the hollow, or depression, too, in
which these muscles are lodged, must have a certain depth; and the
zygomatic arch, under which they pass, must not only have a certain degree
of convexity, but it must be sufficiently strong to support the action of
the masseter.
"To enable the animal to carry of its prey when seized, a corresponding
force is requisite in the muscles which elevate the head; and this
necessarily gives rise to a determinate form of the vertebrae, to which
these muscles are attached, and of the occiput into which they are
inserted.
"In order that the teeth of a carnivorous animal may be able to cut the
flesh, they require to be sharp, more or less so in proportion to the
greater or less quantity of flesh which they have to cut. It is requisite
that their roots should be solid and strong, in proportion to the greater
quantity and size of the bones which they have to break to pieces. The
whole of these circumstances must necessarily influence the development
and form of all the parts which contribute to move the jaws.
"To enable the claws of a carnivorous animal to seize its prey, a
considerable degree of mobility is necessary in their paws and toes, and a
considerable strength in the claws themselves. From these circumstances,
there necessarily result certain determinate forms in all the bones of
their paws, and in the distribution of the muscles and tendons by which
they are moved. The fore arm must possess a certain facility of moving in
various directions, and consequently requires certain determinate forms in
the bones of which it is composed. As the bones of the fore arm are
articulated with the arm bone, or humerus, no change can take place in the
form or structure of the former, without occasioning correspondent changes
in the form of the latter. The shoulder-blade, also, or scapula, requires
a correspondent degree of strength in all animals destined for catching
prey, by which it likewise must necessarily have an appropriate form. The
play and action of all these parts require certain proportions in the
muscles which set them in motion, and the impressions formed by these
muscles must still farther determine the form of all these bones.
"After these observations it will easily be seen that similar conclusions
may be drawn with respect to the hinder limbs of carnivorous animals,
which require particular conformations to fit them for rapidity of motion
in general; and that similar considerations must influence the forms and
connections of the vertebrae and other bones constituting the trunk of the
body, and to fit them for flexibility and readiness of motion in all
directions. The bones, also, of the nose, of the orbit, and of the ears,
require certain forms and structures to fit them for giving perfection to
the senses of smell, sight, and hearing, so necessary to animals of prey.
In short, the shape and structure of the teeth regulate the forms of the
condyle, of the shoulder-blade, and the claws, in the same manner as the
equation of a curve regulates all its other properties; and as, in regard
to a particular curve, all its properties may be ascertained by assuming
each separate property as the foundation of a particular equation, in the
same manner a claw, a shoulder-blade, a condyle, a leg, an arm bone, or
any other bone, separately considered, enables us to discover the
description of teeth to which they have belonged; and so, also,
reciprocally, we may determine the form of the other bones from the teeth.
Thus commencing our investigations by a careful survey of any one bone by
itself, a person who is sufficiently master of the laws of organic
structure may, as it were, reconstruct the whole animal to which that bone
had belonged."