Читать книгу Harper's New Monthly Magazine, No. VI, November 1850, Vol. I - Various - Страница 11

Among the millions of human beings that dwell on the earth, how few are those who think of inquiring into its past history. The annals of Greece and Rome are imparted to our children as a necessary and important branch of education, while the history of the world itself is neglected, or at the most is confined to those who are destined for a scientific profession; even adults are content to receive on hearsay a vague idea that the globe was in being for some undefined period preceding the era of human history, but few seek to know in what state it existed, or what appearance it presented.

This is owing, partly, to the hard names and scientific language in which geologists have clothed their science, and partly to ignorance of the beauty and attractive nature of the study; we dread the long, abstruse-sounding titles of Ichthyosaurus and Plesiosaurus, and are repelled by the dry disquisitions on mineralogy into which professors of the science are apt to stray. The truth is, however, that geology properly is divided into two distinct branches; one of these consists of the less attractive, though equally useful, investigation of the chemical constituents of the strata, and the classification of the fossil flora and fauna which belong to the various formations; this, which may be styled geology proper, is the department which belongs almost exclusively to men of science, and, inasmuch as it involves the necessity of acquaintance with the sister sciences of chemistry, mineralogy, zoology, and botany, is least adapted to the understanding of the uninitiated. The other branch, which may be called the history of geology, presents none of these difficulties; it is as easy of comprehension, and as suitable to the popular mind, as any other historical account; while it presents a variety of interest, and a revolution of events, before which the puny annals of modern history sink into insignificance.

Such of our readers as are unacquainted with the science, will probably be inclined to doubt the possibility of our being aware of events which took place ages before Adam was created; here, however, nature herself steps in, and becoming her own historian, writes "in the living rock" the chronicles of past ages, and so accurately and circumstantially, that we can say positively, "Here existed the sea at such a period, and here the tide ebbed and flowed for centuries;" nay, she shows us the footmarks of extinct animals, and tells us the size, nature, habits, and food of creatures which have for unnumbered ages been buried in the grave of time. She informs us that here the ocean was calm, and that there a river flowed into it; here forests grew and flourished, and there volcanoes vomited forth lava, while mighty earthquakes heaved up mountains with convulsive throes. Such are the events that mark the world's history, and we now purpose giving a short sketch of the various eras in its existence.

Hundreds of thousands of years ago, the earth, now so busy and full of life, rolled on its ceaseless course, a vast, desolate, and sterile globe. Day and night succeeded one another, and season followed season, while yet no living form existed, and still the sun rose upon arid, verdureless continents, and hot, caldron-like seas, on which the steaming vapor and heavy fogs sat like an incubus. This is the earliest period of which we glean any positive record, and it is probable that previous to this era the universe was in a state of incandescence, or intense heat, and that by the gradual cooling of the globe, the external surface became hard, and formed a firm crust, in the same manner that molten lead, when exposed to the cold air, hardens on the surface. The vapors which previously floated around this heated mass, in like manner became partially condensed, and gradually accumulating in the hollows, formed the boiling seas which in after ages were destined to be vast receptacles teeming with life.

How long such a period continued it is impossible to say, and were we even able to number its years, we should in all probability obtain a total of such magnitude as would render us unable to form any accurate idea of its extent. Our ideas of time, like those of space, are comparative, and so immense was this single period in geological history, that any interval taken from human records would fail to present an adequate idea of it.

As might be expected, this era was marked by vast and violent convulsions; volcanoes raged and threw up molten granite, earthquakes heaved and uplifted continents, seas were displaced and inundated the land, and still the earth was enveloped in vapor and mist, arising from the high temperature, and the light most probably penetrated only sufficiently to produce a sickly twilight, while the sun shot lurid rays through the dense and foggy atmosphere. Such a world must have been incompatible with either animal or vegetable life, and we accordingly find no remains of either in the rocks which belong to this early period; their principal characteristic is a highly crystalline appearance, giving strong presumptive evidence of the presence of great heat.

After this era of desolation and gloom, we enter upon what is technically termed the "Transition period," and here we begin to mark the gradual preparation of the globe for the reception of its destined inhabitants. The change is, however, at first very slight, and there is evidence of frequent convulsions and of a high degree of temperature; but the action of fire appears to have declined in force, and aqueous agencies are exerting themselves. The earlier portion of this formation is rendered peculiarly interesting by the fact, that during it the most ancient forms of life sprang into existence. It is true that merely a few species of shell-fish, with some corals, inhabited the depths of the ocean, while the dry land still remained untenanted; nevertheless, humble and scanty as they were, we can not fail to look with interest on the earliest types of that existence, which has subsequently reached such perfection in ourselves.

The presence of corals shows, that although the transition seas had lost their high temperature, yet they retained a sufficient degree of heat to encourage the development of animals requiring warmth. These minute animals possess the remarkable property of extracting from the elementary bodies held in solution in the waters, the materials for forming new rocks. To the coral animalcule or polype we owe much of the vast limestone beds which are found in every part of the world, and many a vessel laden with the riches and productions of the earth finds a grave on the sunken reefs that are the fruit of its labors.

As ages elapsed, and the universe became better adapted for the reception of life, the waters swarmed with zoophytes and corals, and in the silurian strata we find organic remains abundant; shell-fish are numerous and distinct in form, and in some instances display a very interesting anatomical construction. As an instance we may mention the Trilobite, an animal of the crustacean order; the front part of its body formed a large crescent-shaped shield, while the hinder portion consisted of a broad triangular tail, composed of segments folding over each other like the tail of a lobster; its most peculiar organ, however, was the eye, which was composed of four hundred minute spherical lenses placed in separate compartments, and so situated, that in the animal's usual place at the bottom of the ocean it could see every thing around. This kind of eye is also common to the existing butterfly and dragon-fly, the former of which has 35,000, and the latter 14,000 lenses.

Continuing to trace the history of this ancient period, we reach what is called among geologists the Old Red Sandstone age. The corals, and the shell-fish, and the crustacea of the former period have passed away, and in their place we find fishes; thus presenting to us the earliest trace of the highest order of the animal kingdom – vertebrata. The plants in this system are few, and it would seem as if the condition of the world was ill-adapted for their growth. Another peculiar characteristic of this era is the state of calm repose in which the ocean appears to have remained; in many rocks the ripple mark left by the tide on the shores of the ancient seas is clearly visible; nevertheless considerable volcanic action must have taken place, if we are to believe geologists, who find themselves unable to account otherwise for the preponderance of mineral matter which seems to have been held in solution by the waters.

We now pass on to the Carboniferous period, and a marked change at once strikes us as having taken place. In the previous era few plants appear to have existed; now they flourished with unrivaled luxuriance. Ferns, cacti, gigantic equisetums, and many plants of which there are no existing types, grew, and lived, and died in vast impenetrable forests; while the bulrush and the cane, or genera nearly allied to them, occupied the swamps and lowlands. This is the period when the great coal beds and strata of ironstone were deposited, which supply us with fuel for our fires, and materials for our machinery. The interminable forests that grew and died in the lapse of centuries were gradually borne down by the rivers and torrents to the ocean, at whose bottom they ultimately found a resting place. A considerable portion of the land also seems to have been slowly submerged, as in some cases fossil trees and plants are found in an upright position, as they originally grew.

There is no period in geological history so justly deserving of examination as this. To the coal beds then deposited Great Britain in a great measure owes national and mercantile greatness. Dr. Buckland, in speaking of this remote age, remarks in his Bridgewater Treatise, that "the important uses of coal and iron in administering to the supply of our daily wants, give to every individual among us, in almost every moment of our lives, a personal concern, of which but few are conscious, in the geological events of these very distant eras. We are all brought into immediate connection with the vegetation that clothed the ancient earth before one half of its actual surface had yet been formed. The trees of the primeval forests have not, like modern trees, undergone decay, yielding back their elements to the soil and atmosphere by which they have been nourished; but treasured up in subterranean store-houses, have been transformed into enduring beds of coal, which in these latter ages have been to man the sources of heat, and light, and wealth. My fire now burns with fuel, and my lamp is shining with the light of gas derived from coal, that has been buried for countless ages in the deep and dark recesses of the earth. We prepare our food, and maintain our forges and furnaces, and the power of our steam-engines, with the remains of plants of ancient forms and extinct species, which were swept from the earth ere the formation of the transition strata was completed. Our instruments of cutlery, the tools of our mechanics, and the countless machines which we construct by the infinitely varied applications of iron, are derived from ore, for the most part coeval with, or more ancient than the fuel, by the aid of which we reduce it to its metallic state, and apply it to innumerable uses in the economy of human life. Thus, from the wreck of forests that waved upon the surface of the primeval lands, and from ferruginous mud that was lodged at the bottom of the primeval waters, we derive our chief supplies of coal and iron, those two fundamental elements of art and industry, which contribute more than any other mineral production of the earth to increase the riches, and multiply the comforts, and ameliorate the condition of mankind."

This may justly be styled the golden age of the pre-adamite world; the globe having now cooled to a sufficient temperature to promote the growth of plants without being injurious to them, is for the first time clothed in all the rich verdure of a tropical climate. Doubtless the earth would have presented a lovely aspect, had it been possible to have beheld it; the mighty forests unawakened by a sound save that of the sighing of the wind; the silent seas, in which the new-born denizens of the deep roamed at will; the vast inland lakes for ages unruffled but by the fitful breeze; all present to the mind's eye a picture of surpassing, solitary grandeur.

The creatures that existed, though differing from those of the previous age, were still confined to the waters; as yet the dry land remained untenanted. The fishes give evidence of a higher organization, and many of them appear to have been of gigantic dimensions. Some teeth which have been found of one kind, the Megalichthys, equal in size those of the largest living crocodiles.

There is one peculiarity respecting fossil fishes which is worthy of remark. It is that, in the lapse of time from one era to another, their character does not change insensibly, as in the case of many zoophytes and testacea; on the contrary, species seem to succeed species abruptly, and at certain definite intervals. A celebrated geologist18 has observed, that not a single species of fossil fish has yet been found that is common to any two great geological formations, or that is living in our own seas.

Continuing our investigation, we next find the fruitful coal era passing away; scarcely a trace of vegetation remains; a few species of zoophytes, shells, and fishes are to be found, and we observe the impression of footsteps, technically called ichnites, from the Greek ichnon, a footmark. These marks present a highly interesting memento of past ages. Persons living near the sea-shore must have frequently observed the distinctness with which the track of birds and other animals is imprinted in the sand. If this sand were to be hardened by remaining exposed to the action of the sun and air, it would form a perfect mould of the foot; this is exactly what occurred in these early ages, and the hollow becoming subsequently filled by the deposition of new sediment, the lower stone retained the impression, while the upper one presented a cast in relief. Many fossil footmarks have been found in the rocks belonging to this period.

It is evident from the fact of footmarks being found, that creatures capable of existing on dry land were formed about this time, and we accordingly find the remains of a new order – Reptiles. These animals, which now constitute but a small family among existing quadrupeds, then flourished in great size and numbers. Crocodiles and lizards of various forms and gigantic stature roamed through the earth. Some of the most remarkable are those which belong to the genus Ichthyosaurus, or fish-lizard, so called from the resemblance of their vertebræ to those of fishes. This saurian Dr. Buckland describes as something similar in form to the modern porpoise; it had four broad feet, and a long and powerful tail; its jaws were so prodigious that it could probably expand them to a width of five or six feet, and its powers of destruction must have been enormous. The length of some of these reptiles exceeded thirty feet.

Another animal which lived at this period was the Plesiosaurus. It lived in shallow seas and estuaries, and would seem, from its organs of respiration, to have required frequent supplies of fresh air. Mr. Conybeare describes it as "swimming upon, or near the surface, arching its long neck like the swan, and occasionally darting it down at the fish which happened to float within its reach."

This reptile, which was smaller than the Ichthyosaurus, has been found as long as from twelve to fifteen feet. Its appearance and habits differed from the latter materially. The Ichthyosaurus, with its short neck, powerful jaws, and lizard-like body, seems admirably suited to range through the deep waters, unrivaled in size or strength, and monarch of the then existing world; the Plesiosaurus, smaller in size and inferior in strength, shunned its powerful antagonist, and, lurking in shallows and sheltered bays, remained secure from the assaults of its dangerous foe, its long neck and small head being well adapted to enable it to dart on its prey, as it lay concealed amid the tangled sea-weed.

This has been called by geologists the "age of reptiles;" their remains are found in great numbers in the lias, oolite, and wealden strata. These creatures seem to form a connecting link between the fishes of the previous era, and the mammalia of the Tertiary age; the Ichthyosaurus differed little from a fish in shape, and its paddles or feet are not unlike fins, the Plesiosaurus, on the contrary, as its name denotes, partook more of the quadruped form. Dr. Buckland in describing it, says: "To the head of a lizard it united the teeth of a crocodile; a neck of enormous length, resembling the body of a serpent; a trunk and tail having the proportions of an ordinary quadruped; the ribs of a cameleon, and the paddles of a whale." Besides these animals we find the Pterodactyle, half bird and half reptile; the Megalosaurus, or gigantic lizard; the Hylæosaurus, or forest lizard; the Geosaurus, or land lizard, and many others, all partaking more or less of affinity to both the piscatory and saurian tribes.

Passing on now to the period when the great chalk rocks which prevail so much in the southeastern counties of Great Britain were deposited, we find the land in many places submerged; the fossil remains are eminently marine in character, and the earth must literally have presented a "world of waters" to the view. Sponges, corals, star-fish, and marine reptiles inhabited the globe, and plants, chiefly of marine types, grew on its surface. Although, however, a great portion of the earth was under water, it must not therefore be supposed that it was returning to its ancient desolation and solitude. The author whom we last quoted, in speaking of this subject, says: "The sterility and solitude which have sometimes been attributed to the depths of the ocean, exist only in the fictions of poetic fancy. The great mass of water that covers nearly three-fourths of the globe is crowded with life, perhaps more abundantly than the air and the surface of the earth; and the bottom of the sea, within a certain depth accessible to light, swarms with countless hosts of worms and creeping things, which represent the kindred families of low degree which crawl upon the land."

This era seems to have been one of peculiar tranquillity, for the most part undisturbed by earthquakes or other igneous forces. The prevailing characteristic of the scenery was flatness, and low continents were surrounded by shallow seas. The earth is now approaching the state when it will be fit for the reception of man, and in the next age we find some of the existing species of animals.

It is worthy of observation, that at the different periods when the world had attained a state suitable for their existence, the various orders of animal and vegetable life were created. In the "dark ages" of geological history, when the globe had comparatively lately subsided from a state of fusion,19 it was barren, sterile, and uninhabited; next, the waters having become cool enough, some of the lowest orders of shell-fish and zoophytes peopled them; subsequently, fishes were formed, and for ages constituted the highest order of animal life; after this we enter on the age of reptiles, when gigantic crocodiles and lizard-like forms dwelt in fenny marshes, or reposed on the black mud of slow moving rivers, as they crept along toward the ocean betwixt their oozy banks; and we now reach the period when the noblest order of animal life, the class to which man himself belongs, Mammalia, began to people the earth.

The world now probably presented an appearance nearly similar to what it does at present. The land, which in the chalk formation was under water, has again emerged, and swarms with life; vast savannahs rich in verdure, and decked in a luxuriant garb with trees, plants, grasses, and shrubs, and inland lakes, to which the elephant, the rhinoceros, and the hippopotamus, with many extinct races of animals, came to slake their thirst, form the principal characteristics of this period.

There is something peculiarly interesting in looking back to this early age, while Adam was yet dust. We picture to the mind's eye the gigantic Deinotherium, the largest creature of terrestrial life, raking and grabbing with its huge tusks the aquatic plants that grew in the pools and shallow lakes, or, as Dr. Buckland describes it, sleeping with its head hooked on to the bank, and its nostrils sustained above water so as merely to breathe, while the body remained floating at ease beneath the surface. We see its twin-brother in greatness, the Megatherium, as it comes slowly stalking through the thick underwood, its foot, of a yard in length, crushing where it treads, and its impenetrable hide defying the attacks of rhinoceros or crocodile. In the waters we behold the mighty whale, monarch of the deep, sporting in the pre-adamite seas as he now does amid the icebergs of the Arctic ocean; the walrus and the seal, now denizens of the colder climes, mingling with the tropical manati; while in the forests the owl, the buzzard, and the woodcock, dwelt undisturbed, and the squirrel and monkey leaped from bough to bough.

Arrived at the close of the pre-adamite history, after having traced it from the earliest ages of which we possess any evidence, down to the eve of human existence, the reflection that naturally presents itself to the mind is the strangeness of the fact, that myriads of creatures should have existed, and that generation after generation should have lived and died and passed away, ere yet man saw the light. We are so accustomed to view all creatures as created solely for human use, rather than for the pleasure of the Divine Creator, that we can at first scarcely credit the history, though written by the hand of nature herself; and the human race sinks into insignificance when it is shown to be but the last link in a long chain of creations. Nevertheless, that such, however humbling it may be, is the fact, we possess indubitable evidence: and when we consider, as Mr. Bakewell observes, "that more than three-fifths of the earth's present surface are covered by the ocean, and that if from the remainder we deduct the space occupied by polar ice and eternal snows, by sandy deserts, sterile mountains, marshes, rivers, and lakes, that the habitable portion will scarcely exceed one-fifth of the whole globe; that the remaining four-fifths, though untenanted by mankind, are, for the most part, abundantly stocked with animated beings, that exult in the pleasure of existence, independent of human control, and in no way subservient to the necessities or caprices of men; that such is and has been, for several thousand years, the actual condition of our planet; we may feel less reluctance in admitting the prolonged ages of creation, and the numerous tribes that lived and flourished, and left their remains imbedded in the strata which compose the outer crust of the earth."