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Amongthe various pursuits that engage the human mind, there are few so attractive as Geology, none so important as Revelation. Each of these two studies has an interest peculiar to itself. The one is chiefly concerned about the world in which we are living: the other about the world to which we are hastening. Geology leads us down into the depths of the Earth, and there, unfolding to our view a long series of strange unwritten records impressed on lasting monuments by the hand of Nature, it proceeds to trace back the history of our Globe through myriads of ages into the distant past. Revelation, on the other hand, comes to us from above; and setting forth the far more wonderful records of God’s dealings with man, holds out the hope of another world “everlasting inthe heavens”10which shall still remain when this earth and all the works that are therein shall have melted away with fervent heat.11
But, it may be asked, why should two such incongruous topics be set down for discussion side by side? To answer this question is to explain the scope and design of the present work. We are not going to write a Manual of Geology; nor yet a Treatise on Revelation. Taken separately, these two subjects have been handled with eminent skill and ability; the one by the votaries of Science, the other by the friends of Theology. It is our purpose to consider them not so much in themselves as in their mutual relations: to compare the conclusions of Geology with the truths of Revelation; and to inquire if it be possible to accept the one and yet not to abandon the other.
An uneasy apprehension has long prevailed among devout Christians, and a declared conviction among a large class of unbelievers, that the discoveries of Geology are at variance with the facts recorded in the Book of Genesis. Now, the historical narrative of Genesis lies at the very foundation of all Revealed Religion. Hence the science of Geology, has come to be looked on with suspicion by the simple-minded faithful, and to be hailed with joy, as a new and powerful auxiliary, by that infidel party which, in these latter days, has assumed a position so bold and defiant. It is now confidently asserted that we cannot uphold the teaching of Revelation, unless we shut our eyes to the evidence of Geology; and that we cannot pursue the study of Geology, if we are not prepared to renounce our belief in the doctrines of Revelation.
Vet surely this cannot be. Truth cannot be at variance with truth. If God has recorded the history of our Globe, as Geologists maintain, on imperishable monuments within the Crust of the Earth, we may be quite sure He has notcontradicted that Record in His Written Word. There may be for a time, indeed, a conflict between the student of Nature and the student of Revelation. Each is liable to error when he undertakes to interpret the record that is placed in his hands. Many a brilliant Geological theory, received at first with unbounded applause, has been dissipated by the progress of discovery even within the lifetime of its author. On the other hand, it cannot be denied that Theologians have sometimes imputed to the Bible that which the Bible does not teach. Learned and pious men—Protestants and Catholics alike—once believed that the Book of Joshua represents the succession of day and night as produced by the revolution of the Sun around the Earth: whereas it is now considered quite plain that the Book of Joshua, properly understood, teaches nothing of the kind; but that the Inspired Writer, in describing a wonderful phenomenon of Nature, simply employs the language of men according to the established usage of his time. We need not wonder, therefore, that a conflict of opinion should sometimes arise between the Geologist and the Theologian; but a conflict there cannot be between the story which God has described on His works and the story He has recorded in His Written Word.
Though we come forward, therefore, among those whose duty and whose glory it is to uphold Revelation, we are by no means jealous of the wonderful ardor, and we may add, the wonderful success, with which the study of Geology has been lately pursued. We have too much confidence in the truth of our cause to apprehend that it can suffer in any way from the progress of Natural Science. It is our conviction, rather, that the more thoroughly the works of Nature are understood, the more perfectly they will be found to harmonize with the truths of Revelation. We are not afraid, therefore, to venture into the realms of Geology and to come face to face with its discoveries. Too long, perhaps,has this interesting and popular science been neglected by those who are ranged under the banner of Religion. Let it be ours to show that the study of God’s works is not incompatible with the belief in God’s Word; and that it is quite possible to investigate the ancient history of the world we inhabit without forfeiting our right to a better.
The points of contact between Geology and Revelation are chiefly these two:—First, the Antiquity of the Earth; Secondly, the Antiquity of the Human Race. In the present Volume we shall confine our attention to the Antiquity of the Earth. The subject that offers itself for discussion may be stated in a few words. Geologists maintain that the Crust of the Earth has been slowly built up by means of a long series of operations which would require hundreds of thousands, perhaps millions of years for their accomplishment: whereas the Bible narrative, it is alleged, allows but the short lapse of six or eight thousand years from the creation of the world to the present time. The Geological record, then, seems to contradict the Mosaic; and the question is, how this apparent contradiction is to be explained.
Some have ventured to solve the problem by rejecting the historical narrative of the Bible: others by ignoring the plain facts of Geology. But there is a third class of writers, including many names of the highest eminence and authority, who contend that we may admit the extreme Antiquity of our Globe, which Geology so imperatively demands, without compromising in the smallest degree the truthfulness of the Mosaic story. They say that the Chronology of the Bible stops short with Adam, and does not go back to the beginning of the world. By means of the data which the Bible supplies we may calculate, at least roughly, the lapse of time from the Creation of Adam to the Birth of Christ. But from the first beginning of all created things, when God made the Heavens and the Earth, to the close of the Sixth Day when Adam was introduced upon the scene,that is an interval which, in the Bible narrative, is left altogether undefined and uncertain. This is the view which we hope to develop and to illustrate in the course of the following pages.
Our task naturally divides itself into two parts. First, it will be our duty to consider the received theory of Geology, and to examine in detail some of the interesting and wonderful phenomena on which it is founded. This course of investigation, while it is plainly indispensable for the intelligent appreciation of our subject, cannot fail at the same time to unfold many new and striking views of the Power, and the Goodness, and the Providence of God. “For the invisible things of Him from the creation of the world are clearly seen, being understood by the things that are made; even His eternal Power and Godhead.”12
In the Second Part we shall consider the Antiquity of the Earth in reference to the History of Genesis. It will be our purpose to show that, as far as the Bible narrative is concerned, an interval of countless ages may have elapsed between the first creation of the Heavens and the Earth and the beginning of the Six Mosaic Days. Furthermore, we shall contend that, without any prejudice to the Sacred History, we may suppose these Days themselves to have been, not days in the ordinary sense of the word, but long and indefinite Periods of Time. If we succeed in establishing these views, it will be obvious to infer that, while the Bible enables us to determine, at least by approximation, the Age of the Human Race, it allows time without limit for the past history of the Earth.
PART I.GEOLOGICAL THEORY AND THE EVIDENCE BY WHICH IT IS SUPPORTED.
Geology defined—Facts and Theories—Recent progress of Geology—Stratification of Rocks—Aqueous Rocks; of Mechanical Origin—of Chemical Origin—of Organic Origin—Igneous Rocks, Plutonic and Volcanic—Metamorphic Rocks—Summary of the Rocks that compose the Crust of the Earth—Relative order of position—Internal condition of the Globe—Movements of the Earth’s Crust—Subterranean disturbing force—Uplifting and bending of Strata—Denudation and its Causes—Fossil Remains—Their Value in Geological Theory.
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Theobject of Geology is to examine and record the appearances presented by the Crust of the Earth; and by the aid of these appearances, to trace out the long series of events by which it has been brought into its present condition. Geology, therefore, like all other natural sciences, is made up partly of fact, and partly of theory. It belongs to the Geologist first to investigate the phenomena which the Crust of the Earth exhibits to the eye. For this purpose he descends into the mine and the quarry; he visits the lofty cliff by the sea-shore, the deep ravine onthe mountain side, the cutting of a railway; in a word, every spot where a section of the Earth’s Crust is exposed to view, either by the action of Nature or by the hand of man. He then retires into the silence of his closet, with his note-book and his specimens; and there, having arranged and classified the various phenomena which he has already examined with his eyes in the outer world, he proceeds to make his deductions, and to build up his theory. He seeks to explain how materials, so diverse in their composition, have come to be piled up together, with such admirable order, and yet with such endless variety; and how the solid rocks have come to be the repository of petrified trees and plants and bones and shells, which seem, as it were, to start up from their graves, and to tell strange stories of a bygone world.
In the early days of Geology there were comparatively few who devoted themselves with patient industry to the collection and classification of facts: while the number was legion of those who, with a very meagre knowledge of facts, set themselves to build up systems. A vast multitude of different and conflicting theories were, in this way, brought into existence, and attracted for a time much public attention, each one being vehemently defended by its friends and as vehemently assailed by its enemies. These theories resting on no solid foundation, could not hold their ground against the advancing tide of new discoveries. They flourished for a brief space, and then gave way to others scarcely more substantial, which were destined in their turn to be likewise rejected and forgotten. Thus it came to pass, from the manifest instability of its principles, that Geology was long held in light repute, and practical men set little store by its boasted discoveries and startling revelations.
But it would be unjust and unphilosophical to condemn the modern theory of Geologists because of their past errors. We must judge of this science, not according to whatit once was in the feebleness of its infancy, but according to what it now is in the growing strength of its mature years. It seems to be in the nature of things that groundless speculations and wild conjectures go before, and sober Science follows in their wake. The visionary dreams of the Alchemist led the way to the science of Chemistry, and the idle fancies of the Astrologist have given place to the marvellous discoveries of Astronomy. So, too, amidst the confused mass of conflicting arguments and opinions, by which the phenomena of Geology were for a long time enveloped and obscured, the seeds of a new science were slowly germinating. New facts were eagerly sought after to support or to impugn the favorite theory of the hour; and though theory after theory passed away, yet the facts remained. In course of time this accumulation of facts became broad and deep and solid enough to form a sound basis for inductive reasoning; and thus almost within our own days Geology may be fairly said to have assumed the rank and dignity of a science.
During the last quarter of a century it has been studied with a more ardent enthusiasm than, perhaps, any other science in England, in France, in Germany, and in America. It has been studied, too, upon better principles than before: less attention has been paid to the building up of theories, and far more pains and labor have been expended on the careful investigation of natural phenomena. There are still, no doubt, different schools of Geologists which are divided among themselves as regards many important details of theory; but there are some general conclusions upon which all Geologists are substantially agreed, and which, they assure us, are established by evidence that is absolutely irresistible. It is to these conclusions we wish to invite the attention of our readers; for they bear very closely on the question of the Antiquity of the Earth.
Geologists tell us, then, that the materials of which theEarth’s Crust is composed, are not heaped together in a confused mass, but are disposed with evident marks of definite and systematic arrangement. This is an important truth, of which many examples are familiar to us all, though perhaps we do not all attend to their significance. Thus in a quarry, we see commonly enough first a bed of limestone, then above that a bed of gravel, and higher still a bed of clay: and even the limestone itself is not usually a compact mass, but is arranged in successive layers, something like the successive courses of masonry in a building. Now it appears that a very large proportion of the Earth’s Crust is made up in this way of successive layers, orstrata, as they are called by Geologists. Thesestrataare composed of various substances, such as clay, chalk, sand, lime, and coal; and they present everywhere the same general appearances. They are known under the common name of Aqueous Rocks,13because it is believed that they were originally formed under water; and here it is that the professors of Geology first come into collision with the popular notions that formerly prevailed.
They hold that these stratified rocks were not arranged as we see them now, when the Earth first came from the handsof its Creator, but have been formed, during the lapse of unnumbered ages, by the operation of natural causes. Nay more, they have divided the rocks into sundry classes, and they undertake to explain the particular process by which each several variety has been produced. First in order and importance are those which derive their existence from the mechanical force of moving water. The materials of which they are composed first existed in the form of minute particles, which were transported by the action of water from one place to another; then they were spread out over a given surface, just as we now see layers of sand, or mud, or gravel deposited near the mouths of rivers, or in the estuaries of the sea, or even upon the land itself during temporary inundations. Lastly, after a long interval came the slow but certain process of consolidation. The fine sand was cemented together and became sandstone; the loose gravel by a similar process was transformed into a solid mass, known by the name of Conglomerate or Pudding-stone; while the soft mud by simple pressure was converted into a kind of slaty clay, called Shale. Thus from age to age Nature was ever building up new strata, and consolidating the old.
Next in order are the Aqueous Rocks, which owe their origin to the agency of chemical laws. To this class belong many of our limestone formations. Large quantities of carbonate of lime are held in solution by water charged with carbonic acid gas: when the carbonic acid, in course of time, passes off, the carbonate of lime can no longer be held in solution, and it is accordingly precipitated in a solid form to the bottom. In this manner was formed that peculiar kind of limestone called Travertine, which abounds in Italy, and which is well known to all who have visited Rome, as the stone of which the Coliseum was built. A still more familiar example, on a small scale, is seen in the case of Stalactites and Stalagmites. Water saturatedwith carbonic acid trickles down the sides, or drops from the roof of a limestone cavern. In its course it dissolves carbonate of lime, and holds it in solution; afterward, reaching the floor of the cavern, it slowly evaporates and leaves behind it a thin sheet of limestone which is called a Stalagmite; while the icicle-like pendants that are formed by a similar process, on the roof of the cavern, are called Stalactites.
There is a third class of Aqueous Rocks which are supposed to be made up almost exclusively of the fragmentary remains of plants and animals, and are therefore called Organic. The well-known coral reefs, so dreaded by the sailor in tropical seas, are believed to be nothing more than a mass of stony skeletons belonging to the minute marine animalcules known among zoologists as Polyps or Zoophytes. These little creatures, existing together in countless multitudes, extract carbonate of lime from the waters of the ocean in which they dwell, and by the action of their living organs, convert it into a solid frame or skeleton, which is called coral. From generation to generation the same process has been going on during the long succession of Geological ages; and huge masses of coral rock, hundreds of miles in length, have thus been slowly built up from fathomless depths of the ocean to within a few feet of its surface. Our vast coal formations, on the other hand, afford a ready example of rocks which are chiefly composed of vegetable remains.
So much for the Aqueous or Stratified Rocks. Geology next brings before us another and a very different group, of which the origin is ascribed to fire, and which are consequently designated by the title of Igneous Rocks. In their general appearance they are chiefly distinguished from the former by the absence of regular stratification; but they are, nevertheless, intersected by numerous planes of division, or joints, as they are called, and thus divided intoblocks of various size and form. Geologists believe that these rocks were at one time reduced to a molten state by the action of intense heat, and afterward allowed slowly to cool and to crystallize. They are divided into two classes, the Plutonic and the Volcanic. The Plutonic Rocks are chiefly granite of some kind or another; and though they now often appear at the surface, they are supposed to have been produced originally at a considerable depth within the crust of the Earth, “or sometimes, perhaps, under a certain weight of incumbent ocean.”14The Volcanic Rocks have been formed at or near the surface of the Earth, and, as the name implies, they are usually ejected, in a state of fusion, from the fissures of an active volcano; though not unfrequently they assume the more imposing form of basaltic columns, as at the Giant’s Causeway in Ireland, or on the island of Staffa near the coast of Argyleshire in Scotland.
One group of rocks yet remains to be noticed. They have been called by various names at different times, but are now generally designated by the term Metamorphic. In some respects they resemble the Aqueous Rocks, while, in others, they are more nearly allied to the Igneous. Like the former, they are stratified in their outward arrangement; like the latter, they are more or less crystalline in their internal texture. As to their origin, we are told that they were first deposited under water, like the Aqueous Rocks, and that afterward their internal structure was altered by the agency of subterranean heat. Hence the name Metamorphic, first suggested by Sir Charles Lyell, which conveys the idea that these rocks have undergone achange of form. To this group belong many varieties of slate, and also the far-famed statuary marble of Italy.
Our readers will perceive from this brief outline that,if we follow the theory of Geologists, the rocks which compose the Crust of the Earth may be conveniently divided, according to their origin, into three leading groups, the Aqueous, the Igneous, and the Metamorphic. The Aqueous are formed under water, either by the mechanical force of the water itself when in motion, or by the agency of chemical laws, or by the intervention of organic life. Hence they are naturally subdivided into three classes, the Mechanical, the Chemical, the Organic. The Igneous Rocks are produced by heat, being first melted and then allowed to cool. When this process takes place under great pressure in the depths of the Earth, the result is granite; and the granite Rocks are called Plutonic: when near the surface, through the agency of a volcano, the Rocks so formed are called Volcanic. Lastly, the Metamorphic Rocks are nothing else than Aqueous Rocks, of which the texture has been altered by the action of intense heat.
As regards the relative order of position amongst these various classes of rocks, the lowest place seems uniformly to belong to the granitic or Plutonic group. It is true that the granite will often appear at the surface of the Earth; but wherever there is a series of rocks piled one above the other, the granite will always be the lowest. This assertion is based on two broad facts; first, whenever we get to the bottom of the other rocks, they are always found to rest on granite; and secondly, no other rock has ever yet been found beneath it. From this circumstance granite is conceived to be the solid foundation of the Earth’s Crust, and so is often called fundamental granite. Above the granite the Aqueous Rocks have been slowly spread out layer by layer during the long lapse of ages, now in this part of the world, now in that, according as each in its turn was exposed to the action of water. The Volcanic Rocks do not occur in any fixed order of succession. They are distributed irregularlyover almost every country of the globe, occurring sometimes in the form of cone-shaped mountains, sometimes in the form of stately pillars, and sometimes in the form of massive solid walls, called Dykes, forced right through the softer Aqueous Rocks, which were deposited on the surface of the Earth before the eruption. As to the Metamorphic Rocks, which are supposed to owe their peculiar character to the contact of molten mineral matter, wherever they occur, they are found in the immediate neighborhood of some Igneous Rock.
The condition of the Earth beneath its thin external crust has never been the subject of direct observation; for Geologists have never yet been able to penetrate below the granite rocks. Nevertheless, this subject has been often discussed, and has offered a wide field for philosophical speculation. Upon one point all are agreed, that within the Crust of the Earth an intense heat very generally prevails;—a heat so intense that it would be quite sufficient, acting under ordinary circumstances, to reduce all known rocks to a state of igneous fusion. Hence it was a common opinion among the older Geologists that the condition of our globe is that of a vast central nucleus composed of molten mineral, and covered over with a comparatively thin external shell of solid rock. The most eminent Geologists, however, of the present day, hesitate to accept this opinion. They observe: (1) That we have not yet learned what the material is of which the interior of the Earth is composed; therefore we cannot tell for certain what degree of heat is sufficient to reduce that material to a liquid state. (2) It is uncertain how far the immense pressure at great depths may operate to keep matter in a solid state, even when raised to a very high degree of temperature. (3) There are certain astronomical and physical difficulties involved in this theory, which have not yet been fully cleared up. Modern Geologists, therefore, proceeding with more cautionthan their predecessors, while they regard the opinion as probable, refuse to set it down as conclusively demonstrated. But, that a very high temperature prevails in the interior of our globe, is a conclusion, they say, which is established by abundant evidence, and which may be regarded as morally certain.
It may be asked how the various strata of Aqueous Rocks, which constitute the chief portion of the Earth’s Crust, have been lifted up above the level of the sea; for, according to our theory, they were all first deposited under water. This is a question that must inevitably occur to the mind of every reader, and Geologists are ready with an answer. They tell us that from the earliest ages the Crust of the Earth has been subject to disturbance and dislocation. At various times and in various places it was upheaved, and what had been before the bed of the ocean became dry land; again it sunk below its former level, and what had been before dry land became the bed of the ocean. Thus, in the former case a new stratum which had been deposited at the bottom of the sea, with all its varied remains of a bygone age, was converted for a season into the surface of the Earth, and became the theatre of animal and vegetable life: while in the latter case, the old surface of the Earth with its countless tribes of animals and plants,—itsfaunaandfloraas they are called,—was submerged beneath the waters, there to receive in its turn the broken up fragments of a former world, deposited in the form of mud, or sand, or pebbles, or minute particles of lime. Nor is this all; it is but a single link in the chain of Geological chronology. We are asked to believe that, in many parts of the globe, this upward and downward movement has been going on alternately for unnumbered ages; so that the very same spot which was first the bed of the ocean, was afterward dry land, then the bottom of an estuary or inland lake, then perhaps once more the floor of the sea, and then dry land again: and furthermorewe are assured that, while it remained in each one of these various conditions, thousands and thousands of years may have rolled away.
But from what source does that mighty power come which can thus upheave the solid Earth, and banish the ocean from its bed? We are told in reply that this giant power dwells in the interior of the Earth itself, and is no other than the subterranean heat of which we have already spoken. This vast internal fire acts with unequal force upon different parts of the shell or Crust of the Earth, uplifting it in one place, and in another allowing it to subside. Now it is violent and convulsive, bursting asunder the solid rocks, and shaking the foundations of the hills: again it is gentle and harmless, upheaving vast continents with a scarcely perceptible undulation, not unlike the long, silent swell of the ocean. So it has been from the beginning, and so it is found to be even now, in this last age of the Geological Calendar. For even within historic times mountains have been suddenly upheaved from the level plain; and many parts of the Earth’s Crust have been subject to a slow, wave-like movement, rising here and subsiding there, at the rate of perhaps a few feet in a century. Sometimes, too, the fiery liquid itself has burst its barriers, and poured its destructive streams of molten rock far down into the peaceful, smiling valleys.
This theory of an internal disturbing force, which from time to time produces elevations and depressions of the Earth’s Crust, serves to explain another phenomenon, that cannot fail to have struck even the least observant eye. The Aqueous Rocks of mechanical formation are said to have been composed of minute fragments, which were first held suspended in water, and afterward fell to the bottom. If this be true, it follows that these rocks, in the first period of their existence, must have been arranged in beds parallel to the horizon, or nearly so. But we now find them, aseverybody knows, in a great variety of positions: sometimes they are parallel to the horizon, sometimes inclined to it, sometimes at right angles to it; sometimes, too, they are broken right across, sometimes curved and twisted after a very fantastic fashion. Now, all these appearances are the natural results of an upheaving force acting irregularly from below on the solid shell of the Earth. When the subterranean fire is brought to bear equally at the same time on a broad extent of surface, then the overlying strata are bodily lifted up, and preserve their horizontal position. But when the whole force acts with local intensity on a very contracted area, then, at that particular spot, the rocks above will be tilted up, and their position entirely changed. Sometimes they will be only bent and crushed together, sometimes dislocated and turned over; sometimes, perhaps, a mountain will be formed, and the rocks before parallel to the horizon, will afterward remain parallel to the slopes of the mountain.
There is another process known by the name of Denudation, which we cannot pass over in silence, for it occupies a very important place in the Natural History of our globe. Since time first began Denudation has been ever going on at the surface of the Earth, and it has left its mark more or less distinctly upon every group of rocks, from the lowest to the highest. It includes all the various operations by which the old existing rocks are broken up into fragments, or ground into powder, or worn away by friction, or dissolved by chemical action, and then transported from their former site to become the elements of new strata. Hence the name Denudation; since by these operations the former surface of the Earth is carried away and a surface before covered islaid bare. The amount of destruction effected by this process in each successive age is always equal to the bulk of Aqueous Rocks formed within the same time. This will be at once understood when we remember that the Aqueous Rocks are produced, for the most part, by thedeposition of sediment; and sediment is nothing else than the fragments, more or less minute, of pre-existing rocks. What is deposited on the bed of the ocean has been taken from the surface of the land; and the new strata are built up from the ruins of the old. When we see a great building of stone towering aloft to the sky, we are certain that somewhere else on the Earth a quarry has been opened, and that the amount of excavation in the quarry is exactly represented by the bulk of solid masonry in the building. Just in the same way, the mass of Aqueous Rocks is at once the monument and the measure of previous Denudation.
The process of Denudation is the work of many and various natural causes. Heat and cold, rain, hail, and snow, chemical affinities, the atmosphere itself, all have a share in it; but the largest share belongs to the mechanical action of moving water. Every little rill that flows down the mountain side is charged with finely-powdered sediment which it is ever wearing away from the surface of its own bed. Every great stream, besides the immense quantities of mud and sand which in times of flood it carries along in its turbulent course, has its channel strewn over with pebbles at which it never ceases to work, rounding off the angles and polishing the surfaces; and these pebbles, what are they but the fragments of old rocks and the elements of new,—the rubble-stone of Nature’s edifice on its way from the quarry to the building? Then there are those mighty rivers, such as the Amazon, the Orinoco, the Mississippi, the Nile, the Ganges, discharging into the sea day by day their vast freight of mineral matter, millions of cubic feet in bulk, and thousands upon thousands of tons in weight. Often this ponderous volume of mud or sand is carried far out to sea by the action of currents, but sometimes it is deposited near the shore, forming what is called a Delta, and exhibiting an admirable example of stratified rock in the earliest stage of its existence. Lastly, we have to noticethe giant power of the great ocean itself, acting with untiring energies on the coasts of continents and islands all over the world, excavating and undermining cliffs, rolling huge rocks hither and thither, and spreading out the divided fragments in a new order at the bottom of the sea.
To apprehend fully the magnitude of the effects which may fairly be ascribed to this last-mentioned power, we must remember that, according to Geological theory, almost every portion of the Earth’s Crust has been more than once lifted up above the surface of the ocean, and afterward depressed below it. It is believed that this alternate rising and sinking was effected very often, perhaps most commonly, not by sudden convulsions, but rather by slow or gradual movements. Now, during this process, as the land was emerging from the waters or sinking beneath them, new surfaces would be presented in each succeeding century to the force of the ocean currents and the erosive action of the breakers; and it is not difficult to conceive that the accumulated ruins produced, in a long lapse of time, by destructive agents so powerful, so untiring, so universal, may have readily furnished the materials for a very large proportion of the Aqueous Rocks now in existence.
Hitherto we have considered the Crust of the Earth as a great structure slowly reared up by the hand of Nature; we have spoken of the Rocks that compose it, of their origin and history, of the order in which they are disposed, and of the various agencies that have been at work to mould them into their present form and feature. We have now to contemplate this marvellous structure under a new aspect; for we are told by Geologists that it is a vast sepulchre, within which lie entombed the remains of life that has long since passed away. Each series of strata is but a new range of tombs; and each tomb has a story of its own. Here a gigantic monster is disclosed to view, compared to which the largest beast that now roams through the forest is puny inform and contemptible in strength: there, within a narrow space, millions of minute animal frames are found closely compacted together, each so small that its existence can be detected only by the aid of a powerful microscope. In one place whole skeletons are found almost entire, embedded in the bosom of the solid rock; in another, we have a boundless profusion of bones and shells; and again in another, neither the skeleton itself appears, nor yet its scattered bones, but simply the imprint of footsteps once left upon the sandy beach, and still remaining engraved on the stone into which the fine sand has been converted chiefly by the agency of pressure. There is no scarcity of relics in this wonderful charnel-house of Nature. For half a century the work of plunder has been going on without relaxation or remorse; the tombs have been yielding up their dead; every city in the civilized world has filled its museums, and the cabinets of private collectors are overflowing: but the spoils that have hitherto been carried away seem to bear a very small proportion to those which yet remain behind.
These remains of animals and plants embedded in the Crust of the Earth are called Fossils; and Geologists maintain that the Fossils preserved in each group of strata represent the animals and plants that flourished on the surface of the Earth, or in the waters of the ocean, when that group of strata was in process of formation. There they lived, and there they died, and there they were buried, in the sand, or the shingle, or the mud that came down from the waters above. Their descendants, however, still lived on, and new forms of life were called into being by the voice of the Omnipotent Creator, making, as it were, a connecting link between the new age of the world that was coming in and the old one that was passing away. But they, too, died and found a tomb beneath the waters; for Nature, with unexhausted energies, was stillbusy collecting materials from the old rocks, and building up the new. And so that age passed away like the former, and another came; and every age was represented by its own group of strata; and each group of strata was, in its turn, covered over with a new deposit; and the tombs were all sealed up, with their countless legions of dead, their massive monuments of stone, their strange hieroglyphic inscriptions. At length came the last stage of the world’s history, and man appeared upon the scene; and it is his privilege to descend into this wonderful sepulchre, and to wander about amidst the monuments, and to strive to read the inscriptions. In our own days more especially, eager and enthusiastic students are abroad over the whole face of the globe, and are gathering together from every country the Fossil Remains of extinct worlds. By the aid of Natural History they seek to assign to each its own proper place in the ranks of creation; to trace the rise, the progress, and the extinction of every species in its turn; and even to describe the nature and the character of all the various forms of life that have dwelt upon the Earth from the beginning.
Such is the theory of Geology as expounded at the present day by its most able and popular advocates. We have passed over a multitude of minor details that we might not weary our readers, and we have kept aloof from disputed points that we might not get entangled in a purely scientific controversy. Our object has simply been to gather together into a systematic form those more general conclusions which, however startling they may seem to practical men of the world, and even to many of those whose minds have been accustomed to the pursuit of science in other departments, are nevertheless regarded as certain by all who have devoted their lives to the study of Geology. It now remains to investigate the facts on which these conclusions are based, and to consider the line of argument by which somany able and earnest men have been led to accept them. In this vast field of inquiry we shall chiefly direct our attention to those points that bear upon the Antiquity of the Earth; and in attempting to bring home to our readers the nature and the force of Geological reasoning, we shall confine ourselves altogether to simple and familiar illustrations.
Principle of reasoning common to all the physical sciences—This principle applicable to Geology—Carbonic acid an agent of denudation—Vast quantity of lime dissolved by the waters of the Rhine and borne away to the German ocean—Disintegration of rocks by frost—Professor Tyndall on the Matterhorn—Running water—Its erosive power—An active and unceasing agent of denudation—Mineral sediment carried out to sea by the Ganges and other great rivers—Solid rocks undermined and worn away—Falls of the Clyde at Lanark—Excavating power of rivers in Auvergne and Sicily—Falls of Niagara—Transporting power of running water—Floods in Scotland—Inundation in the valley of Bagnes in Switzerland.
I
Inthe physical sciences it is a common principle of reasoning to account for the phenomena that come before us in nature, by the operation of natural causes which we know to exist. Nay, this principle seems to be almost an instinct of our nature, which guides even the least philosophical amidst us, in the common affairs of life. When we stand amongst the ruins of an ancient castle, we feel quite certain that we have before us, not alone the monument of Time’s destroying power, but also the monument of human skill and labor in days gone by. We entertain no doubt that ages ago the sound of the mason’s hammer was heard upon these walls, now crownedwith ivy; that these moss-grown stones were once hewn fresh in the quarry, and piled up one upon another by human hands; and that the building itself was designed by human skill, and intended for the purposes of human habitation and defence. Or, if we see a footprint in the sand, we conclude that a living foot has been there; and from the character of the traces it has left, we judge what was the species of animal to which it belonged, whether man, or bird, or beast. It is true that God is Omnipotent. He might, if it had so pleased Him, have built the old castle at the creation of the world, and allowed it to crumble slowly into ruins: or he might have built it yesterday, and made a ruin begin to be where no castle had stood before; and covered the stones with moss, and mantled the walls in ivy. And as to the footprint in the sand, it were as easy for Him to make the impress there, as to make the foot that left the impress. All this is true: but yet if any one were to argue in this style against us, he would fail to shake our convictions; we should still unhesitatingly believe that human hands once built the castle, and that a living foot once trod the shore.
Now, this principle of reasoning is the foundation on which the ablest modern Geologists claim to build their science. The untiring hand of Nature is ever busy around us: they ask us to come and look at her works, and to judge of what she has done in past ages, by that which she is now doing before our eyes. She is still, they say, building up her strata all over the globe, of limestone, and sandstone, and clay; she is still lifting up in one place the bed of the ocean, and in another submerging the dry land; she is still bursting open the Crust of the Earth by the action of internal fire, disturbing and tilting up the horizontal strata; she is still upheaving her mountains and scooping out her valleys. All these operations are open to our inspection; we may go forth and study them for ourselves; wemay examine the works that are wrought, and we may discover, too, the causes by which they are produced. And if it should appear that a very close analogy exists between these works that are now coming into existence, and the long series of works that are piled up in the Crust of the Earth, it is surely not unreasonable to refer the latter class of phenomena to the action of the same natural causes which we know to have produced the former.
It cannot be denied that this argument is deserving of a fair and candid consideration. Let us proceed, then, to examine how far it is founded on fact, and how far it can be justly applied to the various heads of Geological theory. We will commence with the origin and history of Stratified Rocks; for this constitutes, in a manner, the framework on which the whole system of Geology is supported and held together. It is alleged that the elements of which Stratified Rocks are composed are but the broken fragments and minute atoms of pre-existing rocks, carried off by the agents of Denudation, and spread out over some distant area in regular beds or layers; which, in progress of ages, were slowly consolidated into rocks of various quality and texture. With the view of testing this theory by the light of the principle just explained, we purpose, in the first place, to exhibit some examples of the many forms in which the process of Denudation is going on at the present day all over the world; and afterward, to show that out of the materials thus obtained Stratified Rocks of every description—Mechanical, Chemical, Organic—are being regularly built up in sundry places; and that these correspond in every essential feature with the Stratified Rocks in the Crust of the Earth.
Among the chemical agents of Denudation, there is none more widely diffused than Carbonic acid gas. It is everywhere given out by dead animal and vegetable matter during the process of putrefaction; it is plentifully evolvedfrom springs in every country; and it is emitted in enormous quantities from the earth in all volcanic districts, as well those in which the volcanoes are now extinct as those in which they are active. Now, it is well known from observation, that carbonic acid has the property of decomposing many of the hardest rocks, especially those in which felspar is an ingredient. This phenomenon is exhibited on a large scale in the ancient volcanic district of Auvergne, in central France. The carbonic acid, which is abundantly evolved from the earth, penetrates the crevices and pores of the solid granite, which being unable to resist its decomposing action, is rapidly crumbling to pieces. This mysterious decay of hard rock has been happily called by Dolomieu, “la maladie du granite.”15
Again, all the water which flows over the surface of the land is highly charged with carbonic acid. The rain imbibes it in falling through the atmosphere; and the rivers receive still further accessions from the earth as they pursue their course to the sea. In this combination we discover a powerful agent of Denudation; for limestone rock will be dissolved by water which is impregnated with carbonic acid. Thus all the rivers and streams in the world, when they flow through a limestone channel, are constantly dissolving the solid rock and bearing away the elements of which it is composed. A single example will be sufficient to show the magnitude of the results which are thus produced. It has been calculated by Bischof, a celebrated German chemist, that the carbonate of lime which is carried each year to the sea by the waters of the Rhine, is sufficient for the formation of 32,000,000,000 of oyster shells; or, to view the matter in another light, it would be sufficient to produce a stratum of limestone one foot thick, and four square miles in extent.16If such be the yearly produce ofone river, how great must be the accumulated effects of all the rivers in the world since our planet first came from the hand of its Creator!
Passing from the chemical to the mechanical agents of Denudation, it is worth while to notice the immense power which is often generated by the agency of frost, especially in those countries that are subject to great vicissitudes of heat and cold. During a thaw, water finds its way into the clefts and joints by which all rocks are traversed, and when it is afterward converted into ice, it expands with a mechanical force that is almost irresistible. The hardest rocks are burst asunder, great blocks are detached from the mountain side, and sent rolling down its slopes, or tumbling over crags and precipices, until at length they come to rest in shattered fragments at the bottom of the valley. In this condition they await but the coming of the winter’s torrent to be borne still further on their long journey to the sea.
The fearful havoc done in this way by the alternate action of sun and frost contributes in no small degree to the fantastic and picturesque forms assumed by the mountain peaks of Switzerland. Huge masses of rock have been literally hewn away, until nothing has remained behind but those splintered obelisks and tapering pinnacles so familiar to the eye amidst the sublime scenery of the Alps. Indeed one of the greatest perils encountered by the adventurous spirits whose ambition it is to rival one another in the danger of their exploits, and to climb whatever was before regarded as inaccessible, arises from the enormous fragments of rock which are rent almost unceasingly from the overhanging crags and hurled into the abysses below them. The following incident related by Professor Tyndall is very much to the point. “We had gathered up our things, and bent to the work before us, when suddenly an explosion occurred overhead. Looking aloft, in mid-air was seen a solid shot from the Matterhorn describing its proper parabola throughthe air. It split to pieces as it hit one of the rock-towers below, and its fragments came down in a kind of spray, which fell wide of us, but still near enough to compel a sharp look out. Two or three such explosions occurred afterward, but we crept along the back fin of the mountain, from which the falling boulders were speedily deflected right and left.”
This occurred in 1862, on the occasion of an unsuccessful attempt to reach the highest peak of the Matterhorn. Six years later, when Professor Tyndall at length actually accomplished the object on which he seems to have set his heart, he found the work of destruction still going on. “We were now,” he says in his narrative, “beside a snow-gully, which was cut by a deep furrow along its centre, and otherwise scarred by the descent of stones. Here each man arranged his bundle and himself so as to cross the gully in the minimum of time. The passage was safely made, a few flying shingle only coming down upon us. But danger declared itself where it was not expected. Joseph Maquignas led the way up the rocks. I was next, Pierre Maquignas next, and last of all the porters. Suddenly a yell issued from the leader: ‘Cachez vous!’ I crouched instinctively against the rock, which formed a by no means perfect shelter, when a boulder buzzed past me through the air, smote the rocks below me, and with a savage hum flew down to the lower glacier.”17
Even in our own country, every one is familiar with the efficacy of frozen water in producing landslips. The rain which soaks into the ground in winter, is converted into ice when frost sets in; and upon steep slopes or precipices, its expansive power bursts open the earth, and causes large masses of stones and clay to tumble headlong to the bottom.
But moving water constitutes the most powerful, and, atthe same time, the most universal agent of Denudation. And it is chiefly to the effects of moving water that we mean to direct attention; because its action is more striking to the eye, and more easily understood by the general reader. Every one is aware that the waters of the ocean are constantly passing off by evaporation into the higher regions of the atmosphere, and are there condensed into clouds. These clouds in course of time descend upon all parts of the earth, but especially on the high and mountainous districts. Then rivulets are formed which flow smoothly down the gentle slopes of the undulating country, or plunge headlong over the rocky mountain cliffs; and the rivulets uniting form streams, and the streams, receiving new tributaries as they advance, become rivers; and the rivers flow on to the sea, and discharge each day and each hour their enormous volumes of water back again into the ocean from which they came. Thus all the water of the world is constantly in motion, ever hurrying on, as it were, in one unending round of duty. This is the teaching of daily experience and observation. And we may add, it is the teaching of Sacred Scripture as well. The Wise Man said long ago: “All the rivers run into the sea, yet the sea doth not overflow: unto the place from whence the rivers come, thither they return to flow again.”18
Now, the power of this moving water is a mighty wide-spread agent of change in the physical condition of the globe. For wherever water is in motion over the surface of the land, whether it be a rippling stream, or a mountain torrent, or a majestic river, it is surely wearing away the channel through which it flows, and carrying along in its course particles of clay, or sand, or gravel. This subject is illustrated with great force and great simplicity by Mr. Page. “Every person,” he says, “must have observedthe rivers in his own district, how they become muddy and turbid during floods of rain, and how their swollen currents eat away the banks, deepen the channels, and sweep away the sand and gravel down to some lower level. And if, during this turbid state, he will have the curiosity to lift a gallon of the water, and allow it to settle, he will be astonished at the amount of sediment or solid matter that falls to the bottom. Now, let him multiply this gallon by the number of gallons daily carried down by the river, and this day by years and centuries, and he will arrive at some faint idea of the quantity of matter worn from the land by rivers, and deposited by them in the ocean. In the same way as one river grinds and cuts for itself a channel, so does every stream and rill and current of water. The rain as it falls washes away what the winds and frosts have loosened; the rill takes it up, and, mingling it with its own burden, gives it to the stream; the stream takes it up and carries it to the river, and the river bears it to the ocean.”19
When the current is feeble, the greater part of this earthy material is thrown down upon the way, and forms a stratum of alluvial soil in the bed of the river, and also in the adjoining lowlands, during the time of temporary floods. But when several streams unite, then the carrying power of the current is enormously increased: huge stones are rolled along, and dashed one against another, and broken into fragments, and the fragments are rounded by friction, and become pebbles, and the pebbles become gravel, and the gravel, mud; and the mud is carried on to the mouth of the river, and there falling to the bottom, it forms a tongue of land which is called a delta; or else perhaps it chances to meet with some great ocean current, and then it begins a new journey, and is borne far away to be deposited in the profound and tranquil depths of the sea. It is not,however, mineral matter alone that is transported by the action of rivers. Trees that once were growing on the banks of the stream, and the bones of animals, and human remains, and works of art, are seen floating down with the current, and are found embedded in the sand and mud of the delta at the river’s mouth.
These are some of the actual realities which all may witness, who will go and study for themselves the history of this wonderful element, from the time when it first soars aloft as vapor to the sky, until it returns to the bosom of its parent ocean laden with the spoils of the land. To some of our readers, perhaps, results of this kind may appear insignificant, when considered in relation to the enormous bulk of the stratified rocks. But it should be remembered that the force of which we speak is unceasing in its operation over the whole surface of the earth; and even though the work were small which is accomplished in each successive year, the accumulated effects produced in a lengthened period of time must be immensely great. Besides, it would be a very serious error to form our ideas on this subject, as many would seem to do, from the examples which are to be found within the narrow limits of our own island. We should rather seek for our illustrations among those mighty rivers that drain the vast continents of the world, and exhibit the erosive and transporting power of running water on the grandest scale.
It happens, fortunately for our purpose, that an attempt has been made by scientific men to compute the amount of matter discharged into the sea, by some particular rivers within a given time. For such a computation it is necessary, in the first place, to calculate the volume of water that passes down the channel during that time; and then, by repeated experiments, to ascertain the average proportion of earthy matter which is held suspended in the water. This has been done with the greatest care by the Rev. Mr.Everest, in the case of the river Ganges; and it appears that during the rainy season, which lasts four months every year, from June to September, about 6,000,000,000 cubic feet of mud are carried along by the stream past the town of Ghazepoor, near which the observations were made. Now this enormous bulk of mineral matter would be sufficient to form a stratum of rock one foot in height, and two hundred and eighteen square miles in extent. Or, to adopt the computation of Sir Charles Lyell, the amount which passes by every day is equal to that which might be transported by 2000 Indiamen, each freighted with a cargo of mud 1400 tons in weight. And it is important to remember that this estimate represents but a portion of the sediment which passes into the sea through the channel of the Ganges; for the observations of Mr. Everest were taken at a point which is 500 miles from the sea, and at which the river has not yet received the contributions of its largest tributaries.
We are able, therefore, with some degree of confidence, to estimate the amount of Denudation which is every year effected by the Ganges. And, although the same calculations have not yet been applied with equal care to other great rivers, there is no reason to suppose that the Ganges is an exception. It is asserted on good grounds that the Brahmapootra, which unites with the Ganges close to the Bay of Bengal, carries with it an equal amount of earthy sediment. According to Sir Charles Lyell, the quantity of solid matter brought down each year by the Mississippi amounts to 3,702,758,400 cubic feet. And it is said that 48,000,000 cubic feet of earth aredailydischarged into the sea by the Yellow River in China, called by the natives the Hoang Ho.20Thus year after year the waste of the land iscarried away by rivers, to be spread out over wide areas of the ocean, and perhaps to furnish the materials of future continents.
The effects of running water in wearing away and transporting masses of solid rock are not less deserving of our notice. Every one who has followed the course of a great river when it flows through a rocky channel, must have observed large blocks projecting from the cliffs above, which, having been undermined by the action of the water, seem ready to tumble headlong into the stream; and others lying below, which had fallen before; and others again which had been already carried a considerable distance by the winter’s torrent. Even where the rocks are not displaced, they are gradually being worn away, partly by the friction of the water, but much more by the grinding action of the gravel which the water holds in suspension. Not only is the surface of the rocks thus rounded and polished, but large circular pits, calledpot-holes, are formed by the whirling waters of an eddy carrying round and round a few grains of hard sand.
At the falls of the Clyde near Lanark in Scotland, these various phenomena may be seen to great advantage. Good illustrations are to be found also in many volcanic regions. Some of the larger streams in Auvergne have in course of time forced their way through the solid lava rock, cutting out for themselves channels broad and deep. In Sicily too, we are told, the river Simeto, whose course was blocked up by a current of lava about the beginning of the seventeenth century, has since that time eaten its way through this compact and hardened mass, and now flows on to the sea through a rocky passage forty feet in depth and from fifty to several hundred feet in width.21
But there is no part of the world yet explored where these effects are exhibited on the same gigantic scale as at the far-famedFalls of Niagara. The massive limestone rock from which the waters are precipitated is slowly but certainly disappearing. An enormous volume of water, more than a third of a mile in breadth, plunges in a single bound over a sheer precipice of one hundred and sixty-five feet. The soft slaty rocks upon which the limestone rests are soon eaten away by the action of the spray which rises from the pool below; and then the overhanging cliffs, left without any support, topple over, and are carried off by the torrent. The position of the Falls, therefore, is not stationary, but is receding by very sensible degrees in the direction of Lake Erie, from which the river flows. Speaking of this phenomenon, Sir Charles Lyell observes with much show of reason: “The idea of perpetual and progressive waste is constantly present to the mind of every beholder: and as that part of the chasm which has been the work of the last hundred and fifty years resembles precisely in depth, width, and character the rest of the gorge, which extends seven miles below, it is most natural to infer, that the entire ravine has been hollowed out in the same manner, by the recession of the cataract. It must at least be conceded, that the river supplies an adequate cause for executing the whole task thus assigned to it, provided we grant sufficient time for its completion.”22
With a view to enable our readers to understand more fully the prodigious force which rivers have been known to exert in the transportation of rocks, it may be useful to draw attention to one or two principles of physical science. First, we have the well-known law of Archimedes, thata solid body immersed in a liquid loses a part of its weight equal to the weight of the liquid displaced. Now solid rock as compared with water, bulk for bulk, is rarely more than three times, and often not more than twice as heavy. Consequently,according to this law, almost all rocks will lose a third of their weight, and many will lose one-half, when immersed in water. Again, it has been established thatthe power of water to move bodies that are in it increases as the sixth power of the velocity of the current. Hence, if the velocity of a current is increasedtwo-fold, its moving power will be increasedsixty-four fold; if the velocity is increasedthree-fold, the moving power will be increasedseven hundred and twenty fold; and so on.
From these principles it follows, first, that a much smaller power is required to move a block of stone lying in the bed of a river, than if it were lying on the surface of the land; and secondly, that a very slight increase in the velocity of a current effects a very great increase in its moving power. We need not wonder, then, when we hear of the enormous masses of rocks and trees and mason-work which are carried away even by small rivers in times of flood.23
Here are a few examples. In August, 1829, a fragment of sandstone, fourteen feet long, three feet wide, and one foot thick, was carried by the river Nairn, in Scotland, a distance of two hundred yards. On the same occasion the river Dee swept away a bridge of five arches, built of solid granite, which had stood uninjured for twenty years; the whole mass of masonry sunk into the bed of the stream and was seen no more. And the river Don, as we are assured on the authority of Mr. Farquharson, forced a mass of stones four or five hundred tons in weight up a steep inclined plane, leaving them in a great rectangular heap on the summit. A small rivulet called the College, in Northumberland, when swollen by a flood in August, 1827, “tore away from the abutment of a mill-dam a large block of greenstone-porphyry weighing nearly two tons, and transportedit to the distance of a quarter of a mile.”24But it is needless to multiply examples of phenomena which are occurring every day around us, and of which many among our readers have probably been eye-witnesses.
The transporting power of rivers must not always be estimated by the bulk and velocity of the current; for it is often greatly increased by some accidental obstruction, which for a time blocks up the channel through which the river flows. An instructive illustration is afforded by the river Dranse, which flows through the valley of Bagnes, in Switzerland, and empties itself into the Rhone above the lake of Geneva. In the year 1818 the avalanches which fell down from the mountain side formed a barrier across the valley, and thus effectually blocked up the course of the stream. The upper part of the valley was, in consequence, soon converted into a lake which gradually increased in size as the season advanced. When summer came, and the melting of the snows began, the ice barrier suddenly gave way with a tremendous crash, and the lake was emptied in half an hour. The mass of water, thus in a moment disengaged, burst with destructive violence over the lower valley, sweeping away rocks, forests, houses, bridges, and cultivated lands. Thousands of trees were torn up by the roots, fragments of granite as large as houses were rolled along, and the whole flood presented the appearance of a moving mass of ruins.