The History of Creation.

Vol. II.

by Ernst Haeckel.

CHAPTER XV.

PERIODS OF CREATION AND RECORDS OF CREATION.

Reform of Systems by the Theory of Descent.-The Natural System as a Pedigree.-Palaeontological Records of the Pedigree.-Petrifactions as Records of Creation.-Deposits of the Neptunic Strata and the Enclosure of Organic Remains.-Division of the Organic History of the Earth into Five Main Periods: Period of the Tangle Forests, Fern Forests, Pine Forests, Foliaceous Forests, and of Cultivation.-The Series of Neptunic Strata.-Immeasurable Duration of the Periods which have elapsed during their Formation.-Deposits of Strata only during the Sinking, not during the Elevation of the Ground.-Other Gaps in the Records of Creation.-Metamorphic Condition of the most Ancient Neptunic Strata.-Small Extent of Palaeontological Experience.-Small proportion of Organisms and of Parts of Organisms Capable of Petrifying.-Rarity of many Petrified Species.-Want of Fossilised Intermediate Forms.-Records of the Creation in Ontogeny and in Comparative Anatomy.

The revolutionary influence which the Theory of Descent must exercise upon all sciences, will in all probability affect no branch of science, excepting Anthropology, so much as the descriptive portion of natural history, that which is known as systematic Zoology and Botany. Most naturalists who have hitherto occupied themselves with arranging the different systems of animals and plants, have collected, named, and arranged the different species of these natural bodies with much the same interest as antiquarians and ethnographers collect the weapons and utensils of different nations. Many have not even risen above the degree of intelligence with which people usually collect, label, and arrange crests, stamps, and similar curiosities. In the same manner as some collectors find their pleasure in the similarity of forms, the beauty or rarity of the crests or stamps, and admire in them the inventive art of man, so many naturalists take a delight in the manifold forms of animals and plants, and marvel at the rich imagination of the Creator, at His unwearied creative activity, and at His curious fancy for forming, by the side of so many beautiful and useful organisms, also a number of ugly and useless ones.

This childlike treatment of systematic Zoology and Botany is completely annihilated by the Theory of Descent. In the place of the superficial and playful interest with which most naturalists have hitherto regarded organic structures, we now have the much higher interest of the intelligent understanding which detects in the _related forms_ of organisms their true _blood relationships_. The _Natural System of animals and plants_, which was formerly valued either only as a registry of names, to facilitate the survey of the different forms, or as a table of contents for the short expression of their degrees of similarity, receives from the Theory of Descent the incomparably higher value of a true _pedigree of organisms_. This pedigree is to disclose to us the genealogical connection of the smaller and larger groups. It has to show us in what way the different cla.s.ses, orders, families, genera, and species of the animal and vegetable kingdoms correspond with the different branches, twigs, and groups of twigs of the pedigree. Every wider and higher category or stage of the system (for example a cla.s.s, or an order) comprises a number of larger and stronger branches of the pedigree; every narrower and lower category (for example a genus, or a species) only a smaller and thinner group of twigs. It is only when we thus view the natural system as a pedigree that we perceive its true value. (Gen. Morph. ii. Plate XVII. p. 397.)

Since we hold fast this genealogical conception of the Organic System, to which alone undoubtedly the future of cla.s.sificatory Zoology and Botany belongs, we should now turn our attention to one of the most essential, but also one of the most difficult, tasks of the "non-miraculous history of creation," namely, to the actual construction of the Organic Pedigree. Let us see how far we are already able to point out all the different organic forms as the divergent descendants of a single or of some few common original forms. But how can we construct the actual pedigree of the animal and vegetable group of forms from our knowledge of them, at present so scanty and fragmentary? The answer to this question lies in what we have already remarked of the parallelism of the three series of development-in the important causal relation which connects the palaeontological development of all organic tribes with the embryological development of individuals, and with the systematic development of groups.

In order to accomplish our task we shall first have to direct our attention to _palaeontology_, or _the science of petrifactions_. For if the Theory of Descent is really true, if the petrified remains of formerly living animals and plants really proceed from the extinct primaeval ancestors and progenitors of the present organisms, then, without anything else, the knowledge and comparison of petrifactions ought to disclose to us the pedigree of organisms. However simple and clear this may seem in theory, the task becomes extremely hard and complicated when it is actually taken in hand. Its practical solution would be very difficult even if the petrifactions were to any extent completely preserved. But this is by no means the case. The obvious records of creation which lie buried in petrifactions are imperfect beyond all measure. Hence it is necessary critically to examine these records, and to determine the value which petrifactions possess for the history of the development of organic tribes. As I have previously discussed the general importance of petrifactions as the records of creation, when we were considering Cuvier's merits in the science of fossils, we may now at once examine the conditions and circ.u.mstances under which the remains of organic bodies became petrified and preserved in a more or less recognizable form.

As a rule we find petrifactions or fossils enclosed only in those stones which have been deposited in layers as mud by water, and which are on that account called neptunic, stratified, or sedimentary rocks. The deposition of such strata could of course only commence after the condensation of watery vapour into liquid water had taken place in the course of the earth's history. After that period, which we considered in our last chapter, not only did life begin on the earth, but also an uninterrupted and exceedingly important transformation of the rigid inorganic crust of the earth. The water began that extremely important mechanical action by which the surface of the earth is perpetually, though slowly, transformed. I may surely presume that it is generally known what an extremely important influence, in this respect, is even yet exercised by water at every moment. As it falls down as rain, trickling through the upper strata of the earth's crust, and flowing down from heights into hollows, it chemically dissolves different mineral parts of the ground, and mechanically washes away the loose particles. In flowing down from mountains water carries their debris into the plains, or deposits it as mud in stagnant lakes. Thus it continually works at lowering mountains and filling up valleys. In like manner the breakers of the sea work uninterruptedly at the destruction of the coasts and at filling up the bottom of the sea with the debris they wash down. The action of water alone, if it were not counteracted by other circ.u.mstances, would in time level the whole earth. There can be no doubt that the mountain ma.s.ses-which are annually carried down as mud into the sea, and deposited on its floor-are so great that in the course of a longer or shorter period, say a few millions of years, the surface of the earth would be completely levelled and become enclosed by a continuous sheet of water. That this does not happen is owing to the perpetual volcanic action of the fiery-fluid centre of the earth. The surging of the melted nucleus against the firm crust necessitates continual alternations of elevation and depression on the different parts of the earth's surface. These elevations and depressions for the most part take place very slowly; but, as they continue for thousands of years, by the combined effect of small, interrupted movements, they produce results no less grand than does the counteracting and levelling action of water.

Since the elevations and depressions of the different parts of the earth alternate with one another in the course of millions of years, first this and then that part of the earth's surface is above or below the level of the sea. I have already given examples of this in the preceding chapter (vol. i. p. 361). Hence, in all probability, there is no part of the outer crust of the earth which has not been repeatedly above and also below the level of the sea. This repeated change explains the variety and the different composition of the numerous neptunic strata of rocks, which in most places have been deposited one above another in considerable thickness. In the different periods of the earth's history during which these deposits took place there lived various and different populations of animals and plants. When their dead bodies sank to the bottom of the waters, the forms of the bodies impressed themselves upon the soft mud, and imperishable parts, such as hard bones, teeth, sh.e.l.ls, etc., became enclosed in it uninjured. These were preserved in the mud, which condensed them into neptunic rock, and as petrifactions they now serve to characterise the respective strata.

By a careful comparison of the different strata lying one above another, and the petrifactions preserved in them, it has become possible to decide the relative age of the strata and groups of strata, and to establish, by direct observation, the princ.i.p.al eras of phylogeny, that is to say, the stages in history of the development of animal and vegetable tribes.

The different strata of neptunic rocks deposited one above another, which are composed in very various ways of limestone, clay, and sand, geologists have grouped together into an ideal System or Series, which corresponds with the whole course of the organic history of the earth, or with that portion of the earth's history during which organic life existed. Just as so-called "universal history" falls into larger and smaller periods, which are characterized by the conditions of development of the most important nations at the respective epochs, and are separated from one another by great events, so we also divide the infinitely longer organic history of the earth into a series of greater and less periods. Each of these periods is distinguished by a characteristic flora and fauna, and by the specially strong development of certain vegetable or animal groups, and each is separated from the preceding and succeeding period by a striking change in the character of its animal and vegetable inhabitants.

In relation to the following survey of the historical course of development which the large animal and vegetable tribes have pa.s.sed through, it will be desirable to say a few words first as to the systematic cla.s.sification of the neptunic groups of strata, and the larger and smaller periods corresponding to them. As will be seen directly, we are able to divide the whole of the sedimentary rocks lying one above another into five main groups or periods, each period into several subordinate groups of strata or _systems_, and each system of strata again into still smaller groups or _formations_; finally, each formation can again be divided into stages or sub-formations, and each of these again into still smaller layers or beds. Each of the five great rock-groups was deposited during a great division of the earth's history, during a long _era_ or _epoch_; each system during a shorter _period_; each formation during a still shorter _period_. In thus reducing the periods of the organic history of the earth, and the neptunic strata containing petrifactions deposited during those periods into a connected system, we proceed exactly like the historian who divides the history of nations into the three main divisions of Antiquity, the Middle Ages, and Modern Times, and each of those sections again into subordinate periods and epochs. But the historian by this sharp systematic division, and by fixing the boundary of the periods by particular dates, only seeks to facilitate his survey, and in no way means to deny the uninterrupted connection of events and the development of nations. Exactly the same qualification applies to our systematic division, specification, or cla.s.sification of the organic history of the earth. Here, too, a continuous thread runs through the series of events unbroken. We must therefore distinctly protest against the idea that by sharply bounding the larger and smaller groups of strata, and the periods corresponding with them, we in any way wish to adopt Cuvier's doctrine of terrestrial revolutions, and of repeated new creations of organic populations. That this erroneous doctrine has long since been completely refuted by Lyell, I have already mentioned. (Compare vol. i.

p. 127.)

The five great main divisions of the organic history of the earth, or the palaeontological history of development, we call the primordial, primary, secondary, tertiary, and quaternary epochs. Each is distinctly characterized by the predominating development of certain animal and vegetable groups in it, and we might accordingly symbolically designate the five epochs, on the one hand by the names of the groups of the vegetable kingdom, and on the other hand by those of the different cla.s.ses of vertebrate animals. In this case the _first_, or primordial epoch, would be the era of the Tangles (Algae) and skull-less Vertebrates; the _second_, or primary epoch, that of the Ferns and Fishes; the _third_, or secondary epoch, that of Pine Forests and Reptiles; the _fourth_, or tertiary epoch, that of Foliaceous Forests and of Mammals; finally, the _fifth_, or quaternary epoch, the era of Man, and his Civilization. The divisions or _periods_ which we distinguish in each of the five _long eras_ (p. 14) are determined by the different _systems_ of strata into which each of the five great _rock-groups_ is divided (p. 15). We shall now take a cursory glance at the series of these systems, and at the same time at the populations of the five great epochs.

The first and longest division of the organic history of the earth is formed by the _primordial epoch_, or _the era of the Tangle Forests_. It comprises the immense period from the first spontaneous generation, from the origin of the first terrestrial organism, to the end of the Silurian system of deposits. During this immeasurable s.p.a.ce of time, which in all probability was much longer than all the other four epochs taken together, the three most extensive of all the neptunic systems of strata were deposited, namely, the _Laurentian_, upon that the _Cambrian_, and upon that the _Silurian_ system. The approximate thickness or size of these three systems together amounts to 70,000 feet. Of these about 30,000 belong to the Laurentian, 18,000 to the Cambrian, and 22,000 to the Silurian system. The average thickness of all the four other rock groups, the primary, secondary, tertiary, and quaternary, taken together, may amount at most to 60,000 feet; and from this fact alone, apart from many other reasons, it is evident that the duration of the primordial period was probably much longer than the duration of all the subsequent periods down to the present day. Many thousands of millions of years were required to deposit such ma.s.ses of strata. Unfortunately, by far the largest portion of the primordial group of strata is in the metamorphic state (which we shall directly explain), and consequently the petrifactions contained in them-the most ancient and most important of all-have, to a great extent, been destroyed and become unrecognisable. Only in one portion of the Cambrian strata have petrifactions been preserved in a recognizable condition and in large quant.i.ties. The most ancient of all distinctly preserved petrifactions has been found in the lowest Laurentian strata (in the Ottawa formation), which I shall afterwards have to speak of as the "Canadian Life's-dawn" (Eozoon canadense).

Although only by far the smaller portion of the primordial or archilithic petrifactions are preserved to us in a recognizable condition, still they possess the value of inestimable doc.u.ments of the most ancient and obscure times of the organic history of the earth. What seems to be shown by them, in the first place, is that during the whole of this immense period there existed only inhabitants of the waters. As yet, at any rate, among all archilithic petrifactions, not a single one has been found which can with certainty be regarded as an organism which has lived on land. All the vegetable remains we possess of the primordial period belong to the lowest of all groups of plants, to the cla.s.s of Tangles or Algae, living in water. In the warm primaeval sea, these const.i.tuted the forests of the period, of the richness of which in forms and density we may form an approximate idea from their present descendants, the tangle forests of the Atlantic Sarga.s.so sea. The colossal tangle forests of the archilithic period supplied the place of the forest vegetation of the mainland, which was then utterly wanting.

All the animals, also, whose remains have been found in archilithic strata, like the plants, lived in water. Only crustacea are met with among the animals with articulated feet, as yet no spiders and no insects. Of vertebrate animals, only a very few remains of fishes are known as having been found in the most recent of all primordial strata, in the upper Silurian. But the headless vertebrate animals, which we call _skull-less_, or _Acrania_, and out of which fishes must have been developed, we suppose to have lived in great numbers during the primordial epoch. Hence we may call it after the _Acrania_ as well as after the _Tangles_.

The _primary epoch_, or _the era of Fern Forests_, the second main division of the organic history of the earth, which is also called the palaeolithic or palaeozoic period, lasted from the end of the Silurian formation of strata to the end of the Permian formation. This epoch was also of very long duration, and again falls into three shorter periods, during which three great systems of strata were deposited, namely, first, the _Devonian_ system, or the old red sandstone; upon that, the _Carboniferous_, or coal system; and upon this, the _Permian_ system.

The average thickness of these three systems taken together may amount to about 42,000 feet, from which we may infer the immense length of time requisite for their formation.

The Devonian and Permian formations are especially rich in remains of fishes, of primaeval fish as well as enamelled fish (Ganoids), but the bony fish (Teleostei) are absent from the strata of the primary epoch.

In coal are found the most ancient remains of animals living on land, both of articulated animals (spiders and insects) as well as of vertebrate animals (amphibious animals, like newts and frogs). In the Permian system there occur, in addition to the amphibious animals, the more highly-developed reptiles, and, indeed, forms nearly related to our lizards (Proterosaurus, etc.). But, nevertheless, we may call the primary epoch that of _Fishes_, because these few amphibious animals and reptiles are insignificant in comparison with the immense ma.s.s of palaeozoic fishes. Just as Fishes predominate over the other vertebrate animals, so _Ferns_, or Filices, predominate among the plants of this epoch, and, in fact, real ferns and tree ferns (leafed ferns, or Phylopteridae), as well as bamboo ferns (Calamophytae) and scaled ferns (Lepidophytae). These ferns, which grew on land, formed the chief part of the dense palaeolithic island forests, the fossil remains of which are preserved to us in the enormously large strata of coal of the Carboniferous system, and in the smaller strata of coal of the Devonian and Permian systems. We are thus justified in calling the primary epoch either the era of _Ferns_ or that of _Fishes_.

The third great division of the palaeontological history of development is formed by the _secondary epoch_, or the _era of Pine Forests_, which is also called the mesolithic or mesozoic epoch. It extends from the end of the Permian system to the end of the Chalk formation, and is again divided into three great periods. The stratified systems deposited during this period are, first and lowest, the _Tria.s.sic_ system, in the middle the _Jura_ system, and at the top the _Cretaceous_ system. The average thickness of these three systems taken together is much less than that of the primary group, and amounts as a whole only to about 15,000 feet. The secondary epoch can accordingly in all probability not have been half so long as the primary epoch.

Just as Fishes prevailed in the primary epoch, _Reptiles_ predominated in the secondary epoch over all other vertebrate animals. It is true that during this period the first birds and mammals originated; at that time, also, there existed important amphibious animals, especially the gigantic Labyrinthodonts, in the sea the wonderful sea-dragons, or Halisaurii, swam about, and the first fish with bones were a.s.sociated with the many primaeval fishes (Sharks) and enamelled fish (Ganoids) of the earlier times; but the very variously developed kinds of reptiles formed the predominating and characteristic cla.s.s of vertebrate animals of the secondary epoch. Besides those reptiles which were very nearly related to the present living lizards, crocodiles, and turtles, there were, during the mesolithic period, swarms of grotesquely shaped dragons. The remarkable flying lizards, or Pterosaurii, and the colossal land-dragons, or Dinosaurii, of the secondary epoch, are peculiar, as they occur neither in the preceding nor in the succeeding epochs. The secondary epoch may be called the era of _Reptiles_; but on the other hand, it may also be called the era of _Pine Forests_, or more accurately, of the _Gymnosperms_, that is, the epoch of _plants having naked seeds_. For this group of plants, especially as represented by the two important cla.s.ses-the pines, or _Coniferae_, and the palm-ferns, or _Cycadeae_-during the secondary epoch const.i.tuted a predominant part of the forests. But towards the end of the epoch (in the Chalk period) the plants of the pine tribe gave place to the leaf-bearing forests which then developed for the first time.

SURVEY

_Of the Palaeontological Periods, or of the Greater Divisions of the Organic History of the Earth._

I. _First Epoch_: ARCHILITHIC ERA. _Primordial Epoch._

(Era of Skull-less Animals and Forests of Tangles.)

1. Older Primordial Period or Laurentian Period.

2. Middle Primordial Period " Cambrian Period.

3. Later Primordial Period " Silurian Period.

II. _Second Epoch_: PALaeOLITHIC ERA. _Primary Epoch._

(Era of Fish and Fern Forests.)

4. Older Primary Period or Devonian Period.

5. Mid Primary Period " Coal Period.

6. Later Primary Period " Permian Period.

III. _Third Epoch_: MESOLITHIC ERA. _Secondary Epoch._

(Era of Reptiles and Pine Forests.)

7. Older Secondary Period or Trias Period.

8. Middle Secondary Period " Jura Period.

9. Later Secondary Period " Chalk Period.

IV. _Fourth Epoch_: CaeNOLITHIC ERA. _Tertiary Epoch._

(Era of Mammals and Leaf Forests.)

10. Older Tertiary Period or Eocene Period.

11. Newer Tertiary Period " Miocene Period.

12. Recent Tertiary Period " Pliocene Period.

V. _Fifth Epoch_: ANTHROPOLITHIC ERA. _Quaternary Epoch._

(Era of Man and Cultivated Forests.)

13. Older Quaternary Period or Ice or Glacial Period.

14. Newer Quaternary Period " Post Glacial Period.

15. Recent Quaternary Period " Period of Culture.