Electricity too, in the form of galvanism, has never been idle. We have reason to think that it operates at this moment in acc.u.mulating 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 const.i.tution; 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 ma.s.s 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 ident.i.ty in the nature and laws, not in the intensity, of geological agencies.

_In the fourth place, the laws of zology 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 cla.s.ses. The first cla.s.s 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 cla.s.ses in complexity of organization and strength of the mental powers. The second cla.s.s embraces the mollusks, or animals inhabiting sh.e.l.ls. They are dest.i.tute of a spinal marrow, and for the most part their muscles are attached to the external covering, called the sh.e.l.l, although this sh.e.l.l is sometimes internal. The third cla.s.s 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 cla.s.s have a radiated structure, and often resemble plants, or their habitation is a stony structure. Hence they are sometimes called zophytes, 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 cla.s.ses of animals have existed. But in the earliest times, the three last cla.s.ses--the mollusks, the articulated, and the radiated tribes--vastly preponderated, while the vertebral cla.s.s 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 olite; 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 cla.s.ses, 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 cla.s.ses, by a very decided character. Some of them have distinct flowers, and others are dest.i.tute 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 conifer and cycade, 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 equisetace. More than one third of the entire flora of the secondary formation consists of cycade; 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 cla.s.ses 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 circ.u.mstances, 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 cycade connecting the great families of conifer, or dicotyledons, with the palms, which are monocotyledonous, and the ferns, which are acotyledonous. The chasm, however, between those great and dissimilar cla.s.ses of plants is but imperfectly filled by the few living species of cycade. But of the fossil species. .h.i.therto found above the coal formation, almost one half are cycade; 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 ident.i.ty of former zological 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 cla.s.ses 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 cla.s.ses 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 sh.e.l.ls, furnishes us with an example still more striking. These animals, as they now exist, are divisible into the two great cla.s.ses 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 sh.e.l.ls, 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 pa.s.sed 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 pa.s.s, must not only have a certain degree of convexity, but it must be sufficiently strong to support the action of the ma.s.seter.

"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 vertebr, 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 quant.i.ty of flesh which they have to cut. It is requisite that their roots should be solid and strong, in proportion to the greater quant.i.ty and size of the bones which they have to break to pieces. The whole of these circ.u.mstances 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 circ.u.mstances, 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 vertebr and other bones const.i.tuting 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 a.s.suming 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."

After applying the same principle to animals with hoofs, Cuvier comes to a conclusion even more surprising. "Hence," says he, "any one who observes merely the print of a cloven hoof, may conclude that it has been left by a ruminant animal, and regard the conclusion as equally certain with any other in physics or in morals. Consequently this single footmark clearly indicates to the observer the forms of the teeth, of all the leg bones, thighs, shoulders, and of the trunk of the body of the animal which left the mark. It is much surer than all the marks of Zadig.

"By thus employing the method of observation, where theory is no longer able to direct our views, we procure astonishing, results. The smallest fragment of bone, even the most apparently insignificant apophysis, possesses a fixed and determinate character relative to the cla.s.s, order, genus, and species of the animal to which it belonged; insomuch that when we find merely the extremity of a well-preserved bone, we are able, by a careful examination, a.s.sisted by a.n.a.logy and exact comparison, to determine the species to which it once belonged, as certainly as if we had the entire animal before us. Before venturing to put entire confidence in this method of investigation, in regard to fossil bones, I have very frequently tried it with portions of bones belonging to well-known animals, and always with such complete success, that I now entertain no doubts with regard to the results which it affords."

The remarkable correlation between the parts of existing animals having been thus proved by the most rigid and satisfactory tests, we shall inquire with interest for the result, when Cuvier applied the same principles to the fossil animals. If the laws of anatomical structure were the same when these extinct races lived as they now are, these principles will apply equally well to the bones found in the rocks; and though often only scattered fragments are brought to light, the anatomist will be able to reconstruct the whole animal, and present him to our view. Cuvier was the first who solved this problem. The quarries around Paris had furnished a vast number of bones of strange animals, and these were thrown promiscuously into the collections of that city. Well prepared by previous study, this distinguished anatomist went among them with the inquiry, _Can these bones live?_ The spirit of scientific prophecy was upon him, and, as he uttered his inspirations, _there was a noise, and behold a shaking, and the bones came together, bone to his bone. And the sinews and the flesh came upon them, and the skin covered them._ "I found myself," says he, "as if placed in a charnel-house, surrounded by mutilated fragments of many hundred skeletons of more than twenty kinds of animals, piled confusedly around me. The task a.s.signed me was to restore them all to their original position. At the voice of comparative anatomy, every bone and fragment of a bone resumed its place. I cannot find words to express the pleasure I experienced in seeing, as I discovered one character, how all the consequences which I predicted from it were successively confirmed; the feet were found in accordance with the characters announced by the teeth; the teeth in harmony with those indicated beforehand by the feet; the bones of the legs and thighs, and every connecting portion of the extremities, were found set together precisely as I had arranged them, before my conjectures were verified by the discovery of the parts entire; in short, each species was, as it were, reconstructed from a single one of its component elements."

It is hardly necessary to say that, since this first successful experiment, the same principles have been more thoroughly investigated and extended with the same success into every department of fossil organic nature. The results which have crowned the labors of such men as Aga.s.siz, Ehrenberg, Kaup, Goldfuss, Bronn, Blainville, Brongniart, Deshayes, and D'Orbigny, on the continent of Europe, and of Conybeare, Buckland, Mantell, Lindley, and Hutton, and eminently of Owen, in Great Britain, although sustained by the most rigid principles of science, are nevertheless but little short of miraculous; and they demonstrate most clearly the ident.i.ty of anatomical laws, in all ages, among animals and plants of every size and character, from the lofty lepidodendra and sigillaria to the humblest moss or sea-weed, and from the gigantic dinotherium, mastodon, megatherium, and iguanodon, to the infinitesimal infusoria.

_In the sixth place, physiological laws have always been the same upon the globe._

That death has reigned in all past ages over all animated tribes, as it now reigns, so that in that war there has never been a discharge, I need not attempt formally to prove. For the preserved and petrified relics of all the former races, that now lie entombed in the rocks, furnish a silent but impressive demonstration of the former triumph of that great physiological law, which is stamped by the signet of Jehovah upon all existing organic natures--_Dust thou art, and unto dust shalt thou return._

Scarcely more necessary is it to attempt to show that the same system of reproduction for filling the chasms which death occasions, and which is now universal in the animal and vegetable kingdoms, has always existed.

Indeed, such a system is a necessary counterpart to a system of dissolution. And we find the same phases to this reproductive system in ancient and in modern periods. Organic remains clearly teach us that there have always been viviparous as well as oviparous creatures, and gemmiparous as well as fissiparous animals and plants. The second great physiological law of existing nature has, then, always been the same.

The character of the nourishment by which animals and plants have been sustained has never varied. The latter have ever been nourished by inorganic, and the former by organic, matter. Some animals have ever fed upon the flesh of other animals, as their petrified remains, enclosing the masticated and half-digested fragments of other animals, testify. Other tribes have fed only upon herbs or fruits; and some were omnivorous; just, in fact, as we find the habits of existing animals.

No less certain are we that the processes of digestion and a.s.similation have ever been unchanged. We find the same organs for these purposes as in existing animals, viz., the mouth, the stomach, the intestines, and the blood-vessels, as the coprolites and the cololites abundantly testify. We infer, therefore, with great confidence, the existence of gastric juice and bile for completing the transformation of the food into blood. Indeed, the discovery by a lady (Miss Mary Anning, of England) of that singular secretion from which the color called _India ink_ is prepared, with the ink-bag of the sepia, or loligo, in a petrified state, shows that the process of secretion existed in these ancient animals; and when we find that in all respects their structure was like that of existing animals, although some of the softer vessels have not been preserved, we cannot doubt but the entire process of digestion, and the conversion of blood into bone, nerve, and muscle, was precisely the same as it now is.

In the fact, also, that we find in fossil specimens organs of respiration, such as lungs, gills, and trachea, we learn that the process of a circulation of blood, and its purification by means of the oxygen of the atmosphere, have never varied. Animal heat, too, dependent as it is essentially upon this oxygenating process, was always derived from the same source as at present.

The perfectly preserved minute vessels of vegetables enable us, by means of the microscope, to identify them with the plants now alive; and they prove, too, incontestably, that the nourishment of vegetables has always been of the same kind, and has been converted into the various proximate principles of plants by the same processes.

Again. We have evidence that these ancient animals possessed the same senses as their congeneric races now on the globe. We have one good example in which that most delicate organ, the eye, is most perfectly preserved. It is well known that the visual organ of insects and of crustaceans is composed of a mult.i.tude--often several hundreds or thousands--of eyes, united into one, so as to serve the purpose of a multiplying gla.s.s; each eye producing a separate image of the object observed. Such an eye had the trilobite. Each contained at least four hundred nearly spherical lenses on the surface of the cornea, united into one organ; revealing to us the interesting fact, that the relations of light to animal organization were the same in that remote era as they now are.

But I need not multiply proof of the functional ident.i.ty of organic nature in all ages. It may, however, be inquired, how this ident.i.ty, as well as that of anatomical structure, is reconciled with the great anomalies, both in size and form, which have confessedly prevailed among ancient animals.

Compare the plants and animals which now occupy the northern parts of the globe with those which flourished there in the remote periods of geological history, and can we believe them to be portions of one great system of organic nature?

Compare, for instance, the thirty or forty species of ferns now growing to the height of a few inches, or one or two feet, in Europe and this country, with the more than two hundred species already dug out of the coal mines, many of which were forty to forty-five feet in height; or the diminutive ground pines, and equiseta, now scarcely noticed in our forests, with the gigantic lepidodendron, sigillaria, calamites, and equiseta, of the carboniferous period; and who will not be struck with the great difference between them?

Or go to Germany, and imagine the bones of the dinotherium to start out of the soil, and become clothed with flesh and instinct with life. You have before you a quadruped eighteen feet in length, and of proportional height, much larger than the elephant, and with curved tusks reaching two or three feet below its lower jaw, while no other living animal would be found there larger than the ox, or the horse--mere pygmies by the side of such a monster, and evidently unfit to be his contemporaries.

Again. Let the megatherium be brought back to life on the pampas of South America, and you have an animal twelve feet long and eight feet high, with proportions perfectly colossal. Its fore feet were a yard long, its thigh bone three times thicker than that of the elephant, its width across the haunches five feet, its spinal marrow a foot in diameter, and its tail, where it was inserted into the body, two feet in diameter. What a giant in comparison with the sloth, the anteater, and the armadillo, to which it was allied by anatomical structure!

Still more unequal in size, as compared with living batrachians, was the labyrinthidon, once common in England and Germany, if, indeed, the tracks on sandstone were made by that animal. It was, in fact, a frog as large as an ox, and perhaps as large as an elephant. Think of such animals swarming in our mora.s.ses at the present day!

But coming back from Europe, and turning our thoughts to the animals that trod along the sh.o.r.es of the estuary that once washed the base of Mount Holyoke, in New England, we shall encounter an animal, probably of the batrachian family, of more gigantic proportions. It was the _Otozoum Moodii_, a biped, with feet twenty inches long, more than twice the size of those of the labyrinthidon; yet its tracks on the imperishable sandstone show that such a giant once trod upon the muddy sh.o.r.e of that ancient estuary.

Along that same sh.o.r.e, also, enormous struthious birds moved in flocks, making strides from three to five feet long, with feet eighteen inches long, lifting their heads, it may be, from twelve to eighteen feet above the ground, surpa.s.sing, as it appears, even the gigantic dinornis of New Zealand, now that the feet of the latter have been discovered. I refer to the _Brontozoum giganteum_, whose tracks are so common on the new red sandstone of the Connecticut valley. What dwarfs are we in comparison, who now consider ourselves lords of that valley!

Still more remarkable for peculiarities of structure was the tribe of saurians, which were once so numerous in the northern parts of Europe and America. The ichthyosaurus, a carnivorous marine reptile, sometimes thirty feet long, had the snout of a porpoise, the teeth of a crocodile, the head of a lizard, the vertebr of a fish, the sternum of an ornithorhynchus, and the paddles of a whale. Those paddles, corresponding to the fins of a fish, or the web feet of water birds, were composed, each of them, of more than one hundred bones. In short, we find in this animal a combination of mechanical contrivances, which are now found among three distinct cla.s.ses of the animal kingdom. Its eye, also, having an orbital cavity, in one species, of fourteen inches in its longest diameter, was proportionally larger than that of any living animal.

The plesiosaurus had the general structure of the ichthyosaurus; but its neck was nearly as long as its whole body--longer, in proportion to its size, than even that of the swan.

The iguanodon was an herbivorous terrestrial reptile that formerly inhabited England. It approaches nearest in structure to the iguana, a reptile four or five feet long, inhabiting the marine parts of this continent. Yet the iguanodon was thirty feet long, with a thigh six feet, and a body fourteen feet in circ.u.mference. What an alarm would it now produce, to have such a monster start into life in the forests of England, where no a.n.a.logous animal could be found more than half a foot in length!

Surely this must have been one of the fabulous monsters of antiquity.