1. Length of Geological Time.
To the question, What is the length of geological time, geology gives no definite reply. It establishes only the general proposition that time is long.
The Canon of the Colorado (page 78) is a gorge 200 miles long, bounded the most of the way by steep walls of rock over 3,000 feet in height, cut through sandstones, limestones, and other rocks, and at bottom over parts of it, for several hundred feet, into granite; and above the lofty walls a few miles back from the stream the pile of nearly horizontal strata is continued in mountains to a height of 7,000 to 8,500 feet above the bed of the river. All the facts, as its describers testify, point to running water as the agent that made the great channel. The region was under the sea until the close of the Cretaceous period, for marine Cretaceous strata are the uppermost rocks. It follows, then, that all this extensive excavation was accomplished by slow-acting water during Cenozoic time. Surely Cenozoic time was very long.
The gorge of the Niagara River below the Falls has a length of 7 miles. It is the work of the waters since the middle of the Chain plain period; for in the first place, a former channel leading from the Whirlpool toward Lake Ontario was entirely filled by the gravel and sands thrown in by the melting glacier during the earlier part of that period; and, secondly, Champlain beds containing shells of Lake Erie and a tooth of the Mastodon, formerly spread over the place where the gorge now is, as shown by the remains of the formation above on the Canada side. The water has consequently made this vast excavation, 7 miles long, since Man appeared. The rate of progress of the Falls up stream is not satisfactorily ascertained; the most rapid rate that has been estimated would give more than 30,000 years for the work.
The thickness of a sedimentary deposit is no satisfactory basis for determining the length of time it took to form. In a sea 100 feet deep 100 feet of sediment may accumulate; and the thickness could not exceed this (except a little through wave-action and the winds) if a million of years were given to it.
Let the same region be undergoing a subsidence of an inch a century, and the thickness might increase at that rate; and much faster if a yard a century; and with either rate, giving time enough, any thickness might be attained. Hence a stratum of sandstone 100 feet thick may have been formed in a thousandth part of the time of a thin intervening bed of shale.
Nevertheless, the aggregate maximum thickness which the strata attained during the Several ages may be used for an approximate estimate of the comparative lengths of those ages. On such data, it is deduced that the time-ratio for Paleozoic Mesozoic, and Cenozoic time was not far from 12 : 3 : 1. Consequently, if we suppose the length of time since the Paleozoic began to be 16 millions of years, Paleozoic time will include 12 millions, Mesozoic 3 millions, and Cenozoic I million. Most geologists would make the whole interval several times 16 millions.
2. Progress In Features.
The earth through the ages made progress, -
1. In its surface features: from tile condition of a melted sphere as featureless as a germ, to that of an almost universal ocean with small lands, --enough of land to mark out the feature-lines of the future continents; and at last-after slow expansion southward, a lifting of mountain ranges at long intervals, and a retreating of the waters-to the existence of great continents having high mountain borders and well-watered interior plains.
2. In its river-systems: from the existence of only little streamlets draining small lands in the Archaean and Silurian eras and making no permanent geological record beyond a rain-drop impression; to a condition of vast fresh-water lakes and marshes when beds of vegetable material accumulated for the making of coal-beds; and finally to that of the completed continent, when a single river with its tributaries drains, waters, and contributes fertility to hundreds of thousands of square miles of surface, and the work of fresh waters in rock-making exceeds that of the ocean.
3. In its climate: from a condition of general uniformity of temperature, to, at last,- though with interrupted progress, - that of the present diversity, when the poles have a permanent capping of ice, and only the equatorial regions perpetual verdure.
4. And, again, in its living adornments: from an era when the small rocky lands were bare, or gray and drear with lichens, and all other life was of the simplest kind and below the water-level; to a time of flowerless forests and jungles over immense plains, yet with no sounds from living Nature more musical than tile Amphibian's croak; and onward to the better time when tile earth abounds in flowers and fruits and birds, and is covered with the homes of Man.
3. The System of Nature of the Earth had a beginning and will have an end.
A system of progress or development in the earth as much implies that it had a beginning, as that in any plant or animal. Man, Mammals, Fishes, Mollusks, Rhizopods, Plants, all had, according to geological history, their beginning; so also mountains, valleys, rivers, continents, rocks. And so also the earth ; and therefore the system of nature, whose development went forward in and through it, had its beginning.
If this is true of one sphere in space, we may rightly take another step and assert that the universe had its beginning.
It also admits of demonstration that the earth will have its end. A finished state is always the state before decline and death. The earth is dependent for all the beauty in its living adornments, and even for the. existence of its life, on the heat and light of the sun. The sun is losing annually its heat; and however infinitesimal the amount of loss, it is sure to end in a cooled and dark sun; and hence even long before the sun is cold, the earth, supposing it to have met with no earlier catastrophe, will have become dark and lifeless, literally a dead earth.
4. Progress In Life.
1. The progress in life was in general from the simpler forms to the more complex, or from the low to the high. - This truth has been illustrated in each chapter of the preceding geological history.
2. The progress was by gradual steps. - Species appeared and disappeared, not only at the beginning of ages, or of the subdivisions of a ages called periods, but also during the progress of periods, each of the successive strata containing some fossils not found below, and failing of others, that are abundant in underlying beds. There were at times epochs of widespread catastrophe, ending periods, and two of them, those closing Paleozoic and Cenozoic time, were nearly or quite universal for the continental seas. But these must have left unharmed the life of the deep ocean; and they may not have exterminated 911 the life of the emerged land, or even of the whole area of continental seas.
3. The progress was according, to system. - The first animal life was probably the Protozoan, - or Rhizopods Sponges, and the like; kinds that are minute and destitute of members. But later the four great systems of structure - the Radiate, Mollusk, Articulate, and Vertebrate -were defined; and the species which appeared afterward in the long succession were constructed according to one or the other of these systems. Each system, by the new species that came into existence as time moved on, became displayed in higher and more diversified forms. The first of the Vertebrates were the Fishes, the simplest of its tribes. Even in these limbless species the arms and legs of the higher Vertebrates were present, though only in the state of fins; and the lung, though only as a cellular air-bladder; and the car, though only as a closed cavity containing a loose bone; and so with other parts. Thus the earliest of Vertebrates possessed in an incipient stage many of the organs that became fully developed in the later and higher Vertebrates. And in the succession of species that existed, all. were made on the fish-structure as its basis, even the species of the highest class, - those of Mammals and Man. A zoologist, in order to understand the fundamental elements in the human structure, goes to the fish and the frog for instruction; and Nature is so true to her fundamental principles, that he there finds what he looks for.
4. The system of progress is rightly called a system of development or evolution. - With every step there was an unfolding of a plan, and not merely an adaptation to external conditions. There was a working forward according to preestablished methods and lines up to the final species, Man, and according to an order so perfect and so harmonious in its parts, that the progress is rightly pronounced a development or evolution. Creation by a divine method, that is; by the creative acts of a Being of infinite wisdom, whether through one fiat or many, could be no other than perfect in system, and exact in its relations to all external conditions,-no other, indeed, than the very system of evolution that geological history makes known.
5. The system not one of regular progress upward but one involving the culmination and decline of some tribes as the general unfolding went forward. - As has been brought out in the, history, the division of Trilobites, Brachiopods, and Crinoids, besides others, reached their maximum, or culminated, in Paleozoic time; of Amphibians, in the first period of the Mesozoic era; of Reptiles and Ganoids among Vertebrates, 'and of Cephalopods, the highest of Mollusks, in the later Mesozoic; of brute Mammals, in the period of Cenozoic time. So, again, in the kingdom of plants, the highest Cryptogams - the Acrogens - culminated in the Carboniferous period, that is, the later Paleozoic; Cycads, in the middle Mesozoic; while Palms and Angiosperms have the present era as their time of greatest display and perfection. These are a few examples, showing that progress did not go on regularly upward; but that the- old, not only in species, but also in tribes and orders, were culminating and then passing away, as new and higher tribes were introduced, in the progressing evolution of the kingdoms of life.
6. Parallelism between the progress of the system of life the progress of individual life. - An animal, in its growth from the germ, - or, as it is called, its embryonic development, passes through a succession of forms before reaching the adult state. In Mammals the changes after birth are small, the larger part of them having taken place before birth. But in the lower animals the successive forms are often widely diverse, and they frequently mark successive stages in the life of the animal. Thus, in Insects, there is the caterpillar or grub stage, before the adult; and in many Crustaceans, Mollusks, Worms, and Radiates there are several such stages.
Now species have existed - and many now exist - which have the general characters of the forms in these lower stages ; and, in accordance with the above proposition, the order of their appearance in the geological series is, in general, as announced by Agassiz, that of their development in the embryonic series. Thus, as the worm-like grub precedes the adult insect, so Worms, in geological history, preceded Insects. As a fish-like condition of an Amphibian precedes the adult form in which the fish-like feature is lost, so Fishes preceded Amphibians. The examples of the principle are numerous. Some authors have so great faith in it, that they are ready to decide as to the form of the earliest species of a tribe from the earlier stages in individual development. But this is unsafe, since such forms may have come late, into the system of life as well as early; inasmuch as progress was not ill all cases upward progress.
Where the parallelism above mentioned is not apparent in the general form or structure, it is still manifested in certain Coll comprehensive laws common to both kinds of progress, the geological and embryonic The following lire some Of these laws.
a. The low before the relatively high.
b. The simple before the complex. A germ has little distinction of parts; the animal it is to evolve is there in a very general condition, that is, without any special organs. As development of a Mammal goes on, the defining of the head begins, and this is one of the first steps in the evolving of special parts, or in the specialization of the structure. Protuberances also form and commence the defining of the limbs ; and then, finally, the parts of the limb become distinct, or are specialized. Thus it is throughout the structure, until the specialization of the parts peculiar to the particular animal is completed.
This law of the general before the special is a law also in the geological progress of the system of life. In a fish, the earliest of Vertebrates, the vertebrate structure is exhibited in its most generalized condition. The vertebral column consists of one single uniform range of vertebrae without a neck portion, and without a pelvis to divide the body from a tall and afford support to hind limbs ; the limbs are fins, and hence only rudiments of limbs ; the vertebrae have great simplicity of form; the teeth are all of the simplest kind; the lung is merely all air-bladder, and so oil. Thus, all through the structure, a fish is an exhibition of the vertebrate type in a generalized state. The Vertebrates which succeeded to fishes, the Amphibians, have the grand divisions of the body well brought out, and are specialized also as to limbs even to the toes, and in other ways. Passing onward in time, the new Vertebrates appearing exhibited successively a more and more complete specialization of organs and functions, up to Man. In the development of Man from the embryo, it is not true that he passesthrough a fishlike condition; but it is the case that certain fish-like characteristics may be observed in the structure, during its earlier progress; and one of these is an opening beneath the jaws, which Dr. Wyman has regarded as representative of the gill-openings of Fishes.
This law of progress by specialization has its exceptions; for Snakes, which are limbless, succeeded to higher reptiles which had limbs. But such cases only exemplify another fact, already illustrated, -that, while upward progress was the rule, there was also progress downward, and especially after the time of culmination of a tribe had passed.
c. Stationary forms sometimes before the locomotive. Thus,
(1.) Crinoids, part of the earliest life of the globe, were stationary species living attached by a stem; and, after these, there were free Asterioids. So tile young of the modern Crinoid has a stem for attachment, and loses it, in many species, as it becomes an adult (a Comatulid). (2.) The earliest Brachiopods were attached species, and so are the young of all existing Brachiopods.
d. Forms in a group having the body elongated posteriorly, and endowed behind with locomotive power, generally precede those that are shorter behind and superior in the anterior portion of the body and head, -a headward transfer of the forces of the structure marking all upward progress. The young of a crab has an elongated locomotive tail-extremity, which it loses as it develops to a crab ; and so tile long-tailed shrimps preceded crabs in geological history. The young of a modem Ganoid or gar-pike has an elongated vertebrated tail, which it loses with the change to the adult; and so Ganoids in Palaeozoic time had vertebrated tails, but in Mesozoic time lost them. In the young of some birds the tail segments of the vertebral column are much elongated and free, but, with progressing development, they become greatly contracted, and often consolidated together; and so the earliest Birds, in part, at least, had long vertebrated tails. The young of an Insect is an elongated, worm-like grub; and so Worms preceded Insects. The embryo of Man in an early stage of development has a tail half as long as that of a dog in the same stage.
The principle is a general one through the animal kingdom. This behind is directly connected with, or a consequence of, a transfer forward of the forces of the animal structure by which improvement is given to the anterior extremity, and a higher grade of power and functions to the head. Progress from the embryo in animals is always attended with a gradual improvement of the head extremity, and also with changes of form in adaptation to it; and, parallel with this, progress in the system of animal life, from its earliest beginning, onward, was similarly attended, under all tribes, by a headward transfer of power in the being, and by such structural changes as this involved. Marsh has shown that the Carnivores and Herbivores of the early Tertiary had brains but a half or a third as large in bulk as those nearest related to them in type and size among modern species.
This kind of progress is progress in cephalization; this term being derived from the Greek for head. And the principle here illustrated may be briefly announced as follows: Progress both, in, the system of animal life and in individual life is eminently progress in cephalization.
Man, the last and highest being in the system of life., derives his exalted position from the extreme degree of cephalization which characterizes his structure. Besides having a great brain and great head power, his fore-limbs are removed from the locomotive series, and turned over to the service of the head, and, as is involved in this transfer, his body is erect. Thus, by an abrupt transition, he stands apart from the ape and all brute races.
7. The transitions between species, in the system of progress, not yet proved to be gradual.- The systematic succession in the progress of life, made manifest by facts derived from the rocks, leads many to hold that the whole has been as much a growth under the control of physical law as is proved to be true of the development Of tile earth's features. Geological history has accordingly been appealed to for evidence as whether species, instead of being independent types of structure are so linked together by gradual transitions, that we cannot reasonably avoid the conclusion of their production from one another by gradual change. That evidence it has not yet afforded. This is admitted by all, even by those who believe that the transitions were gradual. Geology has brought to light fewer examples of gradual transition than occur among living species. The wide intervals that have separated related groups are diminished from time to time by the discovery of remains of intermediate species. It has been thus for the interval between the Elephant and Mastodon, and for that between the Horse of modern time and the Tapir-like animals of the early Tertiary (page 204); and the same in many other cases. And yet the new species found have still strong specific differences, and those that have thus far been discovered between the Horse and Tapir are of distinct genera; so that the idea of abruptness between species is riot yet set aside by geological evidence.
But geological evidence on this point is, as has been often urged, far from satisfactory. The record is unquestionably very imperfect. The following are examples.
It is certain that there were birds in the Jurassic period in Europe, for one with its feathers has been found fossil. But thus far we know of but that one specimen out of the many; for if there was one there were myriads.
There, is the same evidence that there were Marsupial Mammals during the Triassic era in North America, and therefore during the Jurassic and Cretaceous eras following; and yet only two jaw-bones of Triassic Marsupials have been found in all the American Mesozoic rocks.
There was abundant life in the oceans of the long Triassic and Jurassic eras; but, nevertheless, not a fragment of any species has been found in the Triassic or Jurassic rocks oil the Atlantic border of North America; and the Triassic of the Rocky Mountain region is as destitute of marine life. The American record respecting marine species of the Atlantic border for the long time between the Carboniferous and Cretaceous eras is utterly a blank.
Again, of the plants of the great forests that covered the American continent in the Triassic and Jurassic eras less than 50 species are known; and yet the whole of the dry land of tile continent must have been covered, and the kinds through. all that time must have been very numerous.
These are examples of the imperfection in the record, and they naturally weaken much the force of geological evidence. But if they weaken it, they do not authorize the conclusion that the transitions were always gradual.
There are some gaps of great width. Of the species connecting Mollusks or other Invertebrates with the first of Fishes, geology has afforded not a fact: it has, found only great Sharks, Ganoids, and Placoderms as the earliest species. With regard to the Palms, which first appeared in the Cretaceous, none of the preceding links have been found; and none for the Elm, Magnolia, and various other Angiosperms that accompanied the first Palms. Bones of true Mamma are very abundant in the Tertiary strata; and yet in the Cretaceous beds, those next earlier, there are numerous remains of great Reptiles, and not a trace, as yet observed, of the true Mammals.
8. Origin of Man.- The interval between the Monkey and Man is one of the greatest. The capacity of the brain in the lowest of men is 68 cubic inches, while that in the highest Man-Ape is but 34. Man is erect in posture, and has this erectness marked in the form and position of all his bones, while the Man- Ape has his inclined posture forced on him by every bone of his skeleton. The highest of Man-Apes, the Orang-utan, cannot walk without holding on by his forelimbs; and, instead of having a double curvature in his back like Man, which well-balanced erectness requires, he has but one. The connecting links between Man and any Man-Ape of past geological time have not been found, although earnestly looked for. No specimen of the Stone age that has yet been discovered is inferior, as already remarked, to the lowest of existing men; and none is intermediate in essential characters between Man and the Man-Ape. Until the long interval is bridged over by the discovery of intermediate species, it is certainly unsafe to declare that such a line of intermediate species ever existed, and as unphilosophical as it is unsafe.
If, then, the present teaching of geology as to the origin of species is for the most part indecisive, it still strongly confirms the belief that Man is not of Nature's making. Independently of such evidence, Man's high reason, his unsatisfied aspirations, his free will, all afford the fullest assurance that he owes his existence to the special act of the Infinite Being whose image he bears.
9. Man the highest species. - It is sometimes queried whether the future may not have its various new species of life, and, among them, some higher than existing Man; whether the age now passing is not to be followed, as was true of the Carboniferous, or the Reptilian, by another still more glorious in its living species; whether, if one of the great Dinosaurs of the Mesozoic age could have thought about his own and other times, he would not have imagined his age the last and the best possible, and whether Man is not playing as foolish a part in styling himself the "lord of creation."
Against the introduction of new species in coming time science has little to urge. But there is strong reason for holding that, whatever the changes in the lower tribes, existing Man will always remain the highest in the series.
(1.) Science has made known that the highest of species next to Man, that is, the brute Mammals, have already passed their maximum (page 225); hence, the rest of time remains for the culmination of the only higher type, that of Man. And, as this type includes now but one species, we have reason for expecting no new species in the future.
(2.) From geological history we learn also that the type of Vertebrates commenced in kinds that were horizontal in attitude,- the Fishes; and that from the horizontal there was, Reptiles and Mammals, a raising of the head above the line of the body, up to the Ape, in which the attitude is nearly vertical; and finally, to perfect verticality in Man, a being having the head placed directly over the body and hind limbs. Thus, as Agassiz observed, the last term in the series has been reached; there can be nothing beyond. This is true as to the general type of structure; but it leaves it an open question whether there may not be other species of Man, or erect beings, of still higher grade.
(3.) But a different species of Man higher than existing Man is not a possibility. We can conceive of other species of Man distinguished by having some of the external features of the Man-Apes. But these are marks of inferiority, and, if possible in a type of so high grade, could belong only to inferior species.
The increasing erectness and breadth of forehead in Man, and the shortening of the jaws, giving a nearly vertical line to the front, which are a known result of culture, indicate the course which upward progress must take. And in these points and some others closely related, the limits of perfection have been nearly reached by some among the present race. Further improvement can give physically only larger capacity to the brain and greater beauty of form to the whole structure, and make these qualities more general. No wide divergence from existing Man can be conceived of. When all possible change in these directions has been accomplished, Man will still be Man, and no more the head of the system of life than he is at present.
(4.) Beyond all this we may say, that since no Dinosaur, and no other species but Man, has ever been capable of reviewing the past or contemplating the future; and since Man not only has all time and all Nature within the range of his thought and study, but can even yoke Nature for service, and in fact has her already at work for him in numberless ways, - the system with such a head must be complete.
Nature, through Man, has attained to the possession of a living soul capable of putting her once wasted energies into strong and combined movement for social, intellectual, and moral purposes, and this is the consummation that the past has ever had in prospect.
The Man of the future is Man triumphant over dying Nature, exulting in the freedom and privileges of spiritual life.