Significance of fossil remains—Science of PalÆontology—Classification of existing animal life—Fossil remains are found to fit in with this classification—Succession of organic life—Time in Geology not measured by years and centuries—Successive periods marked by successive forms of life—The Geologist aims at arranging these periods in chronological order—Position of the various groups of strata not sufficient for this purpose—It is accomplished chiefly through the aid of fossil remains—Mode of proceeding practically explained—Chronological table.

The existence of Fossil Remains is, then, a fact. Go where you will through the civilized world, and every chief town has its Museum, into which they have been gathered by the zeal and industry of man; descend where you can into the Crust of the Earth,—the quarry, the mine, the railway cutting,—and there, notwithstanding the plunder which has been going on for two centuries or more, you will find that the inexhaustible cabinets of Nature are still teeming with these remains of ancient life.

When we are brought, for the first time, face to face with these countless relics of a former world, we are impressed with a sense of wonder and bewilderment. That the skeletons before us, though now dry and withered, were once animated with the breath of life; that the trees now lying shattered and prostrate, and shorn of their branches, once flourished on the earth, we cannot for a moment hesitate to believe. But beyond this one fact, all is darkness and mystery. These gaunt skeletons, these uncouth monsters, these petrified forests, are silent, lifeless, as the rocks within whose stony bosoms they have lain so long entombed. Had they speech and memory, they could tell us much, no doubt, of that ancient world in which they bore a part, of its continents, and seas, and rivers, and mountains; of the various tribes of animals and plants by which it was peopled; of their habits and domestic economy; how they lived, how they died, and how they were buried in those graves from which, after the lapse of we know not how many ages, they now come forth into the light of day. As it is, however, we can but gaze and wonder. We have nothing here but the relics of death and destruction: there is no feeling, no memory, no voice, in these dry bones; no living tenant in these hollow skulls, to recount to us the history of former times.

So thinks and reasons the ordinary observer. But far different is the language of the Geologist. These dry and withered bones, he tells us, are gifted with memory and speech; and, though the language they speak may seem at first unfamiliar and obscure, it is not, on that account, beyond our comprehension. Like the birds, reptiles, fish, and other symbols, inscribed on the obelisks of ancient Egypt, these bones and shells stored up in the Crust of the Earth, have a hidden meaning which it is the business of Science to search out and explain. They are Nature’s hieroglyphics, which she has impressed upon her works to carry down to remote ages the memory of the revolutions through which our Globe has passed; and when we come to understand them aright, they do unfold to us the story of that ancient world to which they belonged.

The interpretation of Fossil Remains is, then, an important department of Geology. Of late years it has been admitted to the rank of a special science, under the name of PalÆontology, which means, as the word denotes—pa?a??? ??t?? ?????—the science which is concerned about the organic remains of ancient life. The honor of having been the first to place this science on a solid basis, in fact we may say the honor of having brought it into existence, is justly accorded to the distinguished Cuvier, whose name shed a lustre upon France during the early years of the present century. It is therefore still in its infancy; but it has already rewarded the zeal of its students by many wonderful and unexpected revelations. We purpose in the first place to examine the principles on which it is founded, and then to take a rapid glance at the conclusions to which it has led.

At the outset it is worthy of notice that the very existence of Fossil Remains, buried deep in the Crust of the Earth, forcibly confirms the Geological theory of Stratified Rocks. These rocks, as the reader will remember, are said to have been slowly spread out, one above another, during the lapse of many ages, by the operation of natural causes; and we have seen how this doctrine is supported by arguments founded on an examination of the rocks themselves,—of the materials that compose them, and of the way in which these materials are piled together. Now let us observe how clearly the testimony of Fossil Remains seems to point in the same direction.

First, the bones and shells which we now find in such profusion, far down beneath the superficial covering of the Earth, must have belonged to animals which, when living, flourished on what was then the surface. Yet now they are buried in the bosom of the hard rock, and covered over with beds of solid limestone, and sandstone, and conglomerate, hundreds and thousands of feet in thickness. How can we explain this fact, unless we suppose that these animals, when they perished, were embedded in some soft materials, which afterward became consolidated, and above which, in the course of ages, more and more matter was deposited, until at length that lofty pile of strata was produced, beneath which the remains are now found buried?

Again, it is part of our theory that the formation of Stratified Rocks took place, for the most part, under water. The Organic Remains, therefore, which we should naturally expect to find preserved in the strata of the earth, would be those of aquatic animals; or, if the remains of land animals were to be looked for, it should be of those chiefly which live near the banks of rivers and estuaries, and which, after death, might have been carried down by the current and buried in the silt and mud with which almost all rivers are charged at certain seasons of the year. We know as a fact that such animals are buried at the present day in the Deltas of the Ganges and the Mississippi; and it would be reasonable to suppose that the same should have occurred in former ages. Now here again the evidence of Fossil Remains exactly fits in with our theory. For the vast bulk of them are manifestly the remains of animals that lived in water: and the terrestrial animals, comparatively few, whose bones are preserved in the Crust of the Earth, are such as frequent the banks of great rivers or the marshy swamps of estuaries.

Thus much we may learn even from a cursory glance at Fossil Remains. But these curious monuments of ancient times have a deeper meaning, which cannot be unfolded without a more minute and laborious investigation. Our readers are aware that all the animals at present existing on the face of the Earth have been scientifically grouped together, according to certain well-marked characteristics, into various Kingdoms, Classes, Genera, and Species. Thus, for example, the horse and the dog are two different Species, belonging to the same Class of Mammalia; the eagle and the sparrow are two different Species of the same Class called Birds. Then again the Class of Mammalia and the Class of Birds both belong to the one common Kingdom of Vertebrata; because, though different in many other respects, they agree in this, that all the members of both Classes have a vertebral or spinal column, to which the other parts of the internal skeleton are attached.

Now when Cuvier began to examine closely the Organic Remains of former times, to which his attention was called by the bones dug up in the gypsum quarries of Montmartre, near Paris, about the close of the last century, he brought with him to the task a very large acquaintance with the various forms of life that, in the present age, prevail throughout the world. And he was greatly struck with the marked difference between those living animals with which he had been long familiar, and those with which he now became acquainted for the first time. The more he extended his researches, the more manifest did this difference appear; until at last it became quite clear that the great bulk of the animals whose remains are preserved in the Crust of the Earth, have no representatives now living on its surface. Nevertheless, he observed that, though the Species no longer exists, it often happens that we have still other Species of the same Genus; or if the Genus, too, be extinct, we have other Genera of the same Class. Here, then, is the first great truth at which Cuvier arrived, and which has been since confirmed by extensive observations:—that the animals which formerly dwelt on this Earth of ours, were, for the most part, widely different from those by which it is now inhabited: and yet there is a well-defined likeness between them; that both have been created on a plan so strictly uniform, that the one and the other naturally find their place in the same system of classification.

As the science of PalÆontology progressed, and new facts were day by day accumulated, another truth, not less important, was gradually but certainly developed. In the distribution of Fossil Remains through the various strata of the Earth, there is a certain order observed, a certain regular law of succession, which cannot have been the mere result of chance, and which it is the business of science to unravel and explain. The facts are these. If we follow a particular set of strata in a horizontal direction, we find that the same fossils continue to prevail over hundreds of square miles, nay, often over a space as large as Europe, though beyond certain limits this uniformity of Fossil Remains will gradually be observed to disappear. But when we penetrate in a vertical direction through the strata, the forms of animal and vegetable life that we meet with are constantly changing. After a few hundred yards at the most, we find ourselves in the midst of a group of fossils, altogether different from those which we have passed in the beds above: and so on, as we proceed downward, each particular set of strata is found to have an assemblage of fossils peculiar to itself.82

There can be no reasonable doubt as to the truth of these facts. They have been established and confirmed by the positive testimony of a whole host of Geologists, whose researches have extended to all parts of the globe. And we have besides a kind of negative evidence on the subject which is scarcely less convincing than the positive. Nothing is more easy than to refute a universal proposition if it is false. If it is not a fact that each group of strata, as we proceed downward, exhibits a collection of Fossils peculiar to itself, the assertion may be at once disproved by pointing out two or three different groups with the same Fossils. There are thousands of practical Geologists at work all over the world, eager for fame; and any one of them would make his name illustrious if he could overturn a theory so generally received. Now, when a statement of facts can be easily disproved if untrue; and when, at the same time, there is a large number of men whose interest it would be to disprove the statement if possible; and when it is nevertheless not disproved; this circumstance, we contend, is a convincing argument that the alleged facts are true. And such precisely is the case before us. We therefore think it would be unreasonable not to accept the facts.

Let us next examine what is their significance. Each group of strata, be it remembered, represents to us the animal life that flourished on the Earth during the period in which that particular group was in progress of formation. It is, as it were, a cabinet in which are preserved for our instruction certain relics or memorials of that age in the world’s history. Of course it is not a perfect collection; but only a collection of those remains that chanced to escape destruction, and by some natural embalming process to be saved from dissolution. When we learn, then, that there is a marked uniformity in the assemblage of Fossils that are spread over a large horizontal area, in any group of strata, we conclude that, when that group was in course of formation, there was a certain uniformity in the animal life that extended over the corresponding area of the globe; just as, at the present day, the same species of animals are found to flourish over a great part of Europe, or America. And if this uniformity of Fossil Remains does not extend horizontally to an indefinite distance, this is precisely what we should have expected from the analogy of the existing creation: for, when we examine the present distribution of animal life over the earth, we find a marked diversity to exist between countries that are removed from one another; as, for instance, between Europe and Australia.

In the next place, we are told that, as we proceed downward into the Crust of the Earth, each successive group of strata has an assemblage of Fossils clearly distinct in character from those of the group above and of the group below. The conclusion to which this fact points is obvious enough. If, in the former case, we inferred that the animal life of any one period, considered in itself, was the same over extensive areas, in this case we must infer that the animal life of each successive period was peculiar to that particular age; being altogether distinct in its character from the animal life of the period that went before and of the period that followed. It would appear, therefore, as Sir Charles Lyell puts it, “that from the remotest period there has been ever a coming in of new organic forms, and an extinction of those which pre-existed on the earth; some species having endured for a longer, others for a shorter time; while none have ever reappeared after once dying out.”83

Now, from these principles, Geologists have been gradually led to build up a system of Geological Chronology; in other words, to determine the order of time in which the numerous groups of strata that make up the Crust of the Earth have been formed, and thus to fix the age of each group in reference to the rest. This Chronology is not reckoned by the common measures of time which are used in history, but rather by the successive periods during which each group of rocks was in its turn slowly deposited on the existing surface of the globe. For example, the Coal-measures that so abound in the North of England are very much older than the bluish clay of which London is built. But if we ask what is the difference between the age of the one and of the other, the answer is given not in days and years and centuries, but in the number of different Formations that intervened between the two. We are told that the Coal-measures belong to the Carboniferous Formation; that this Formation was followed by the Permian, and that again in succession by the Triassic, the Jurassic, and the Cretaceous; and that, upon this last was spread out the Eocene, to which the London clay belongs. Indeed, as regards the precise length of any given period, Geologists can offer nothing but the wildest conjectures. Some form their estimates in thousands of years; others in millions. And the wisest amongst them fairly confess they have no sufficient data to make an accurate computation. Nevertheless, they are all agreed in this, that the ages of which the memory is preserved in history, that is to say, the last six thousand years, are but a small part of one Geological period. Compared to the voluminous chronicles laid up in the Crust of the Earth, the records inscribed by human hands constitute but an insignificant fraction of the world’s history. Our readers will be glad to learn something of the way in which this startling system of Geological Chronology is constructed and developed.

At first sight, perhaps, it might be imagined that the order of time in which the various strata were deposited, can be easily learned from the relative position in which they lie. Since each stratum, when first produced, was spread out on the existing surface of the globe, it is clear that the one which lies uppermost in the series must be the newest, then that which lies next below, and so on till we reach the lowest of the pile, which must be the oldest of all. Nothing could be more satisfactory than this reasoning, if each stratum was spread out over the whole Earth, and if, after having been once deposited, it was never afterward removed. We might then regard each stratum as a volume in the Natural History of the Globe, which, when it was finished, was laid down upon that which contained the chronicles of the preceding age; and thus the position of every stratum would be in itself a sufficient evidence of the age to which it belonged.

But such is not the case. Nowhere does the Crust of the Earth exhibit a complete series of the Stratified Rocks laid out one above another. In any given section we can find but a few only of the long series of groups that are familiar to Geologists. And if we follow them on, in a horizontal direction, we shall invariably find that some of the strata will thin out and disappear, while new strata will gradually be developed between two groups that were before in immediate contact. Let it be observed, in passing, that this fact fits in most perfectly with the theory we have been all along defending. The Stratified Rocks were deposited under water; therefore, the strata of any given period were not spread out over the whole Globe, but at most over those parts only which, for the time, were submerged. With the next period came a change in the boundaries of land and water; and the formation of strata ceased in some localities and began in others: and so on from epoch to epoch. Thus the areas over which the process has been going on, have been, in every age, of limited extent, and have been ever shifting from place to place over the surface of the earth. Moreover, there is the opposite process of Denudation. Many of the strata deposited in the depths of the ocean must have been afterward swept away by the breakers, as they slowly emerged from the waters; or at a later time, reduced to their original elements, and carried back to the sea, by the action of rivers, rain, and frost. It should seem, therefore, as well from the fact, which is obvious to any one who will examine it, as from our theory, which harmonizes so completely with the fact, that the strata which we meet with in any given section of the Earth’s Crust present to us but a very broken and imperfect series of monuments. They are, as it were, but odd volumes of a long series, and though they lie in juxtaposition, they may belong, nevertheless, to Geological epochs widely removed from each other.

Hence, in order to construct a complete system of Geological Chronology it is necessary to collect together these odd volumes, as they may be called, of the Great Geological Calendar, and to assign to each one its proper place in the series. This difficult and complicated task is accomplished chiefly by the aid of Fossil Remains. We have already shown that the Fossil Remains which are found embedded in each group of strata, represent the organic life of the period during which that group of strata was in progress of formation. Moreover, we have seen that each period was marked by the existence of an animal and vegetable creation peculiar to itself. If, therefore, we find that the Fossils of two different districts exhibit the same general character, we may conclude that the beds in which they are preserved were deposited about the same age, and consequently belong to the same Geological Period. Whereas, on the other hand, if, within certain limits, we discover two groups of strata, each of which has a collection of Fossils totally different from the other, it is a proof that these two groups were not deposited in the same age, and must, consequently, be referred to different Epochs of the Geological Calendar. Let us now see in what manner the practical Geologist proceeds to apply these general principles.

He takes first some one country, say England, and in that country he selects some one particular district to begin with. Here he examines a number of different sections, and makes himself familiar with all the strata of the neighborhood, and with the order in which they lie. Let us suppose that he finds three different groups spread out one above another, and let us call these groups A, B, and C; A being the lowest, B immediately above A, and C above B. The chronological order of these strata will be, therefore, A, B, C. He will study next the Fossil Remains which he finds embedded in each group. For convenience we may designate the Fossils of A by the letter a, those of B by b, and those of C by c. Now, according to the principles above explained, these three collections of Fossils will be specifically distinct from one another, each collection being characteristic of one particular set of strata. Our Geologist next goes into a neighboring district, and there examines a number of sections as before. Let us suppose that he encounters again the groups A and B. He may, perhaps, have been able to trace the beds from one district to the other, by observations made upon his line of route: or it may be that the nature of the country has rendered such observations impossible; or the observations may have been so imperfect that from them he could arrive at no certain conclusion regarding the identity of the strata. But, at all events, if the new district yield an abundant supply of Fossils, he cannot long be at a loss. He will recognize the group A by the Fossils a, and the group B by the Fossils b. An important fact, however, soon attracts his attention. Group C has entirely disappeared, and is not to be found in this district; while between A and B there is a new group of rocks that he has not seen before, with a collection of Fossils different from a, b, and c. We will call this new group X, and its Fossils x. It is clear that the formation of X must have intervened between the formation of A and B; and the chronological order now stands A, X, B, C. In like manner another district may disclose a fourth group of strata, say Y, intervening between B and C. The chronological order will then stand A, X, B, Y, C. And thus the Geologist pursues his explorations until he has gone through the whole country, and arranged the principal groups of strata according to the order of time in which they were deposited.

In this way the whole of England has been minutely explored during the last half century. The task was first undertaken by William Smith, who is justly called the Father of English Geology. After multiplied researches, extending over a space of many years, during which he travelled the whole country on foot, this eminent man published in 1815 his Geological Map of England and Wales with part of Scotland; a work which is described by Sir Charles Lyell as “a lasting monument of original talent and extraordinary perseverance.” Hundreds followed in the same course, exploring every day new districts, and, by the new facts which they brought to light, supplying what was wanting in the work of Smith, correcting what was faulty, and confirming what was true; until at length, in our day, it may be said that the Stratified Rocks of England are almost as well known and as completely mapped out as are its counties and its towns, its rivers, lakes, and mountains.

Meanwhile, Geologists were not idle in other parts of the world. Germany, France, Italy, even many districts of America and Australia, have been diligently explored according to the same principles as England. And by a comparison of the observations made, the Chronological order of strata over a considerable part of the Earth, but more particularly of Europe, has been now pretty fairly ascertained. This order we have attempted to set forth in an intelligible and sensible form by means of the table here annexed.

In the Woodcut are represented the strata hitherto examined by Geologists, laid out one above another, according to the order of time in which they are supposed to have been produced. The whole series is divided into a number of Formations, the names of which are given in the first column, together with an approximate estimate of their thickness, in feet. These Formations are distinguished from each other in the drawing by a difference of shading. Each of them, according to Geological theory, is believed to have come into existence by the accumulation of solid matter at the bottom of the sea; and the Period of time occupied in its production is usually designated by the same name as the Formation itself. Thus we read of the Carboniferous Formation and the Carboniferous Period: by the former phrase is meant certain groups of strata contemporaneously deposited over various parts of the Earth’s surface; and by the latter, the Period of time during which these groups of strata were spread out. In like manner, when we hear of the Carboniferous Fauna and Flora, we are to understand the animal and vegetable life that flourished during the Carboniferous Period. And again, when Geologists talk of the Cretaceous sea, and tell us that it rolled over a great part of what is now called Europe, they mean to speak of that sea on the bottom of which the Cretaceous rocks were deposited.

Most of the Formations comprise various groups of strata; and these groups are made up of different varieties of rocks, which are again divided into layers or beds of varying thickness. Even in these beds themselves we can often distinguish an indefinite number of laminÆ or plates, scarcely thicker than a sheet of paper, which correspond to the periodical depositions of matter by which the rock was originally formed. These numerous subdivisions may be conveniently illustrated from the Carboniferous Formation. It is divided into two leading groups of strata; the Mountain Limestone below, the Coal Measures above. The upper group is the larger as well as the more important. It attains a maximum thickness in South Wales of 12,000 feet; and consists of numerous strata of Sandstone and Shale, with thin seams of Coal occasionally interposed. In one remarkable instance a hundred distinct layers of Coal, varying in thickness from six inches to ten feet, have been counted in one Coal-field, each resting on a bed of Shale, called in mining phraseology the Underclay. This Shale itself naturally divides into an indefinite number of thin plates, just like the stratum of mud accumulated by the annual inundations of the river Nile, and constituting the present soil of Egypt.

We have not attempted to represent in our Woodcut these various divisions and subdivisions of Stratified Rocks. But the names of some important and well-known groups we have had engraved, to impress more vividly on the mind the place to which they are to be referred in the Geological Calendar. Thus the reader may see at a glance the respective ages of the Coal and the Chalk; of the Lias, in which are preserved the remains of extinct gigantic reptiles, and the Glacial Drift, in which the elephant, the rhinoceros, and the hippopotamus are found entombed; of the Mountain Limestone, which is often nothing else than vast beds of Coral uplifted from beneath the waters of the ocean, and the Oolite, which includes the Portland quarries, where the petrified stems of ancient forest trees are found standing erect in the solid rock.

As the series of Stratified Rocks is divided by Geologists into a certain number or systems or Formations, so these are again grouped into still larger classes, called Primary, Secondary, and Tertiary; that is to say, first, second, and third, in the order of formation. These larger classes correspond to the Great Epochs or Ages of Geological time, each comprising within itself many distinct Periods. The Primary rocks are also called PalÆozoic—pa?a???, ancient, and ????, an organic being—because they contain the oldest forms of organic life: in like manner the term Mesozoic—es??, middle, and ????—is applied to the Secondary strata, inasmuch as they contain the middle or intermediate forms of organic life: and the name Kainozoic—?a????, new, and ????—is given to the Tertiary, which contain the newest forms of organic life.

The term Post-Tertiary has recently been adopted to designate those superficial deposits which are subsequent to the Tertiary Age. They are divided into two groups; the Recent, which corresponds with the period of history, and the Post-Pliocene which precedes it. Some writers seem to think that these deposits, being so very insignificant and so very modern when compared with the long series of Stratified Rocks, are not truly Geological. But this, we should say, is a mistaken view of the question. It seems to us that even the minute layer of mud that is deposited every day at the mouth of the Ganges or the Mississippi, is linked on to the long chain of events which have brought the Crust of the Earth into its present condition; and, therefore, truly belongs to the science of Geology, and is deserving of its proper place in Geological classification.

We may here observe that the names of the great Geological Epochs are descriptive names; that is to say, the obvious meaning of the words corresponds to the character of the strata they are used to represent. Primary, Secondary, Tertiary, mean First, Second, and Third, in the order of formation: PalÆozoic, Mesozoic, and Kainozoic, signify that the strata so called are characterized by Ancient, Middle, and Modern, forms of organic life. But it is very often quite otherwise with the names of the several Formations: and this is a point of no small importance to the student of Geology. These names must be regarded simply as names employed to designate the strata formed in each successive period, and not exactly to describe their character. They generally had their origin in some accidental circumstance, or were derived from some particular locality; and afterward, being perpetuated, gradually came to receive a much more extended application than that which the words themselves would seem to suggest. Thus, for instance, the Cretaceous Formation is so called from the remarkable stratum of white chalk (creta) which was deposited during that period over a great part of Europe; but it would be a mistake to suppose that the whole Formation is made up of chalk. On the contrary, in different localities it is composed of very different materials; near Dresden, for example, it is a gray quartzose sandstone, and in many parts of the Alps it is hard compact limestone.84 Again, the Devonian Formation derives its name from Devonshire, where the rocks of the Devonian period were first minutely examined; but we must not therefore infer that this Formation is peculiar to the county of Devon; it is to be found in many other parts of England, also in Ireland, and on the continent of Europe. So, too, another Formation has received the name of Carboniferous, which literally means Coal-bearing (carbo fero) because of the beds of Coal which are sometimes associated with its strata; yet this Formation is often found quite destitute of Coal over a very extensive area.

In looking over our Table of strata the reader must have noticed that the successive spaces in the Woodcut are not proportioned to the actual thickness of the successive Formations for which they stand. The Secondary and Tertiary Rocks taken together are scarcely one-third as thick, in reality, as the Primary; yet they occupy an equal space in the engraving: and, more remarkable still, the Cretaceous system is allowed double the space of the Laurentian, though less than half as thick. This circumstance calls for a passing word of explanation. In the early annals of a country there is generally a great scarcity of authentic records; and, from a simple dearth of facts, the history of a whole century is compressed, not unfrequently, into a few pages: whereas, in later times, when documentary evidence begins to accumulate, the historians will often spread out the events of two or three years over several chapters. Something of the same kind takes place in Geology. The Fossil Remains, from which, as from authentic documents, the Geologist chiefly derives his information regarding the history of the Earth’s Crust, are scanty in the earlier Formations, and abundant in the more recent. And thus it happens that the older Geological Periods, notwithstanding the vast thickness of the rocks by which they are represented, do not occupy a very prominent position in the annals of Geology, and are compressed into a comparatively insignificant space in its Tables. Nevertheless, the immense depth of the earliest Stratified Rocks must be taken into account in any attempt to estimate the comparative duration of the several Geological Periods. We have, therefore, set down, under the name of each Formation, an approximate estimate of its actual thickness, taken chiefly from the works of Doctor Haughton and Sir Charles Lyell.

Before bringing this chapter to an end we would observe that the system of classification we have here endeavored to explain does not pretend to be final and complete. It is, on the contrary, little more than a temporary expedient to render intelligible the results at which Geologists have hitherto arrived; and is liable to manifold modifications in proportion as their acquaintance with the records they have undertaken to interpret becomes more extensive and more minute. All that they now contend for is this: that the successive Formations represent successive Periods of time, which followed one another in the order here set forth, and during which the Earth was peopled with certain species of Plants and Animals, for the most part peculiar to their respective eras.85