Part 13

Rivers and streams are constantly exerting a mechanical action on the surfaces over which they run; abrading and tearing off fragments even of the hardest rocks, they roll them in their course until the velocity becomes insufficient to transport them farther. At diminished velocities they move fragments of less size, down to the smallest pebbles; at still less velocities, they transport sand, and finally earthy matter, in the most minute division. These are deposited in succession in positions corresponding to the rapidity of the stream, and hence the beds of rivers present at each of their different sections, materials of magnitude and quality corresponding to the rate at which the stream usually flows. The increase in the magnitude of streams, due to violent rains and the melting of the snows, changes the position of the substances that compose their bed, and the more easily suspended materials are often held until the stream actually meets the ocean. In such sudden increases, the streams often overflow their usual banks, and make their deposits laterally, until the constant succession of such deposits raises the adjacent ground high enough to set bounds to the further spreading of the stream. This deposit is remarkable for its taking place in greatest quantity close to the usual bed of the stream; and thus it speedily opposes natural dykes to its own redundant waters. This action is most conspicuous at points where marked changes take place either permanently or periodically in the rapidity of running water: when streams descend from mountains into lines of less descent, a deposit uniformly takes place, forming _flats_ or _intervals_, as they are styled in the United States, of which we have such beautiful instances in the valleys of the Connecticut and Mohawk, and that part of the Hudson near Albany; again, where rivers meet the sea, they are interrupted in their course by the rise of the tides of the ocean, and here again deposits take place, sometimes forming shoals and banks in the ocean itself; at other times, bars and obstructions at their own mouths; and again, deltas of solid land, constantly encroaching upon the sea. This action, which is continually going forward, is called alluvial. The delta of greatest fame, and from which the others have derived their generic name, is that of the Nile; this we have evidence, almost historic, to prove to be wholly the gift of the river. And if it no longer increase as rapidly as in former ages, the cause is obvious, for the alluvion has been pushed so far forward as to meet a strong current that sweeps along the African coast, and must carry off much of the earth the Nile discharges into the Mediterranean. The great rivers of Asia and of America carry still greater quantities of solid matter, but we have not the same distant traditions to refer to for the amount of the increase they have caused; still, however, we know that the mouth of the Mississippi has been advanced into the Gulf of Mexico several leagues since the settlement of Louisiana; and that islands of great extent are frequently formed, in the course of a single year, by the deposits of the Ganges.

We however find traces of aqueous action far more extensive and powerful than those which are now taking place under our eyes by fluviatile action. There is no part of the globe that has been examined, which does not show that it has been subjected to the action of water, in floods far more powerful than any we now are in the habit of seeing. Every where, except in the case of rocky cliffs, and steep mountains, or where we see obvious evidence of a recent elevation, we find the surface strewn with the deposits of water: boulders of greater or less size, beds of gravel, sand, and clay, form the present outer coating of the greatest part of the land. These deposits were long confounded with the alluvial, but have at length been proved, by incontrovertible evidence, to be the results of an action, which if not contemporaneous, must have been universal. We have seen an able attempt to show that this species of deposit did not take place at one and the same period, but was merely the general consequence of similar causes acting at different epochs. Our impression, we must however confess to be, that the action was not only co-extensive with the globe, but contemporaneous. It at any rate exhibits proofs the most satisfactory, that the last great and extensive change which our earth has undergone, was effected by the agency of water, in a state of rapid and violent motion. Ascribing this deposit to a single flood, it has been styled diluvial.

There are cases where alluvial deposits rest upon the diluvium, and from the depth of these it has been attempted to calculate the time that has elapsed since the former of these actions was resumed. The diluvium has also been found in caverns lying upon an ancient stalagmite, and covered again with a new formation of that modification of carbonate of lime. The thickness of the latter deposit has also been made the basis of a calculation, and although neither of these methods is to be considered as approaching to an accuracy more perfect than some hundreds of years, the two methods confirm each other in the general result, which is, that, at a date not more remote than fifty or sixty centuries, there must have taken place a total submersion of all the land, except, perhaps, the tops of high mountains, did they then exist. We have in the sacred volume, a record of such a catastrophe, the flood of Noah, and from that time to the present, no convulsion, equally extensive in its influence, has devastated the globe. Have not then the geologists who have seen in these indications the convincing evidence of that occurrence, been warranted in their inference, of the identity of an event pointed out by undeniable physical evidence, with one recorded in a history to which one of the most confirmed sceptics has recently admitted the merit of truth?

The diluvial deposits are found not only in the lower grounds, but on the tops and sides of lofty mountains; we have ourselves noted them distinctly characterized at high elevations upon the Kaatskills; they are found among the Alps at Valorsine, 6000 feet above the level of the sea, and in another place at more than 7000 feet. The excavations made in the extension of the city of New-York at Corlaer's Hook, have laid open a vast mass of diluvium, and afforded means for studying it with great facility. It in fact presented the appearance of a great cabinet of specimens of primitive and transition rocks, and it was possible in many cases to determine the very mountain whence the fragments had been torn. The most remarkable boulder, for instance, of a weight of at least an hundred tons, was distinctly recognisable as identical in every respect with the granitic syenite of Schooley's mountain, distant at least forty miles. Others had no known type nearer than Connecticut, in the opposite direction, while the gneiss and mica slate of the island of New-York, with their various embedded minerals, the serpentine and many of the magnesian minerals of Hoboken, with sandstone and trap of the Pallisadoc range, were distinctly recognisable. In this great excavation, where a region of a mile square was wholly removed, to a depth, in many places, of thirty feet, no animal remains, as far as can be learnt, were detected; thus marking a most important difference between these deposits and those of the Old continent. Such is the remark of an intelligent geologist, whom we are proud to reckon as our _collaborateur_, and to whom that branch of Natural History is under no small obligations.

"Fragments of granite and other primitive rocks, cast here and there upon stratified formations, and interpersed in diluvium,[10] present a fact as certain as it is astonishing. All the chains of Mount Jura, all the mountains that precede the Alps, the hills and plains of Germany and Italy, are strewn with blocks of granite, often of a great dimension, and always of a composition as pure, and as perfect a crystallization, as the granites of the higher Alps. The same phenomenon is repeated in the plains of Russia, of Poland, of Prussia, of Denmark, and of Sweden. From Holstein to Eastern Prussia, diluvial[11]grounds, sand and clay, are covered with an immense number of blocks of granite. Near the island of Usedom, several points of granite rock rise from the bottom of the Baltic. We see in like manner, Scania and Jutland so filled with these fragments, that they construct of them enclosures, houses and churches. In the Lymfiord, a gulf of Jutland, and at some places on the western side of that peninsula, great points of granite rise from the bottom of the waters. But what is still more remarkable, is to see immense masses of granite lying on the tops of Roeduburg and Osmond, which are more than 6000 feet in height, and are therefore among the highest mountains in the North of Europe."

Beneath the diluvial deposit, we find beds and strata of substances of different character, and which appear on a cursory view to be involved in inextricable confusion. Long and careful examination has at length been efficient in ascertaining that in this apparent disorder are to be seen the traces of an order, as perfect as that of any other mechanism of nature, and of a succession of changes by which the earth has been finally fitted for the habitation of man. These strata have been finally arranged into five distinct classes, differing in their characters and position. These have been so fully described in a former article in this Journal, by the distinguished associate whom we have already quoted, that no more remains for us to say, than what is merely necessary to keep up the connexion of our subject.

These stratified rocks or formations are remarkable for the regular order in which they succeed and overlie each other, furnishing distinct and indisputable evidence of their having been formed in succession. The first set of strata, which are never covered by any of the others, and hence are conceived to be of most recent formation, lie inclined at a small angle to the horizon. In many cases they do not assume the character of rocks, but although distinctly stratified, are often soft and friable, presenting beds of marle and clay, and thick deposits of sand. In some cases their appearance is so similar to diluvial or even alluvial deposits, that they might be mistaken for them, were it not for their more regular stratification. These are the tertiary formations of the German school, the superior order of Coneybeare and Philips.

Issuing from beneath these, and forming in their turn a considerable portion of the surface of the earth, rising occasionally into considerable hills, are strata of less uniform and regular inclination, forming basins and cavities in which the tertiary deposits are often found to lie, curved to conform to the bottoms of these basins.

The third and fourth series issue in their turn from beneath the preceding, as does the fifth from beneath the fourth. Each is marked in succession, by a greater degree of confusion or distortion in the stratification, until the last, which is apparently upheaved and thrown about without any regularity, its strata being occasionally found in positions almost vertical. Not only is the succession of the five different orders of rocks constant, but so is that in which the several rocks of each series overlie each other. This regularity of succession is, however, subject to this law; namely, that rocks of particular orders, or even the whole order itself, may be wanting in particular districts; thus, tertiary formations may be directly upon the lower order, and the second, third, and fourth, may not be present; or any one of the higher orders may lie directly upon any one of those we have stated to be inferior to it; but it has never been observed that the arrangement itself has been inverted, or that a rock which is in one place inferior, becomes, in its turn, superior in another.

The fifth, or inferior order, is uniformly found beneath one or all of the others; and, we may infer, that it in fact underlies the whole surface of the globe, forming not only the foundation of the solid land, but the original bottom on which the present bed of the sea is deposited. The rocks that compose this series are all highly crystalline in their character, are mostly composed of substances wholly or nearly insoluble in water, are wholly devoid of organic remains, and are in fact such substances as might be supposed to have been formed by slow cooling, from a state of igneous fusion. Is it then assuming too much to infer, that they are in fact the crust which has been first formed upon the surface of the earth, intensely heated by its own condensation, under the action of the gravitating force, that, communicated to it by the hand of the Creator, determined its figure, and still maintains its equilibrium. We do not include in this class, as is usually done, the crystalline rocks not stratified, as we conceive them to have been formed in another manner, to which we shall hereafter refer. All the four higher series of strata show, in the most evident manner, that their formation has been due to the action of water; the grauwacke is, perhaps, the only rock that exists among them, in which the question could, even on simple inspection of specimens, appear doubtful; but this rock lies at the base of the old red sandstone, and upon the limestone of the submedial order, or transition, as it is styled by the Wernerians, and is equally regular in its stratification with either; we cannot, therefore, admit any other cause of its formation than what is common to them.

Some of these strata are obviously mechanical, others chemical deposits; thus, the sandstones and conglomerates are certainly the products of the disintegration of older rocks by a violent abrasion of running water, and have settled when the currents have ceased to flow; all calcareous rocks, except the limestones of the inferior or fifth order, the primitive of Werner, on the other hand, appear to have been products of chemical precipitation; while there are a few cases, as in the beds of rock salt, where the deposit must have been due to evaporation.

Of all these rocks and formations, the primitive, as has already been stated, and the sandstones, are wholly devoid of organic remains. And even the last rule is to be received as not wholly free from exception; for vegetable impressions have been found, as we are credibly informed, in sandstone, at Nyack on the Hudson, and near Belleville in New-Jersey, besides some other similar cases we shall hereafter note. All the other strata present a greater or less abundance of the traces of the organic kingdoms, from the slate, which lies lowest of the fourth order, to the most recent beds of the tertiary, and to so much of the diluvium as has been examined in the old continent. And although in the isolated case of the diluvium at New-York, no fossil remains have been found, we are yet unprepared to admit this as more than an exception, and are inclined to think that the remains of the mastodon, for instance, must be diluvian, or pre-diluvian. In this opinion, however, we know that we are opposed by high authority, and therefore do not express it without hesitation.

"Organized fossil remains belong to three different classes: the remains that have preserved their natural state, at least in part; petrifactions; and impressions.

"The remains of the first class are principally bones, and even entire skeletons, which, after having been stripped of the skin and flesh that covered them, have remained, some buried in the earth, others hidden in deep caverns. They are, sometimes, calcined in whole or in part, without having lost their configuration; they at others preserve, not only their texture, but even some traces of their hair and skin. They are also occasionally seen covered with a calcareous crust.

"Petrifactions, to use this word in its familiar sense, include all stony bodies that have the figure of an organized body. There are cases in which a strong solution has penetrated into a cavity formed by an organic body that has disappeared. Then the strong substance has occupied the cavity that has been left empty, and has taken the external form of the body that formerly existed there. If this body were, for instance, a branch or trunk of a tree, the stone will have at its surface its knots and asperities; but within, it will present all the characters of a true stone; it will be no more, to use the language of Hauy, than the statue of the substance that it has replaced.

"At other times, a vegetable or animal substance, while undergoing decomposition in a successive manner, and by obvious degrees, is pressed by the petrifying liquid that already surrounds it. As soon as an organic particle has disappeared, its place is occupied by one of stone."

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"Metallized bodies, and those which have been changed into bitumen or carbon, belong to this system of formation; thus, the turquoises, for instance, are the teeth of a great marine animal; a metallic substance has penetrated them, and has gradually replaced the softer parts of the bones.

"Impressions are often found between the plates of slaty rocks; they are relievos or intaglios representing the skeletons of animals, particularly fish, leaves, seeds, and entire plants, of which the most common kind belong to the forus."

The impressions of vegetables are most abundant in the shales that accompany coal formations; those of leaves and branches are the most common, but there are a few instances in which they retain the delicate structure of the flowers. All analogy leads to the inference, that those now found in temperate climates, are of such a character as could only exist in tropical regions; and when, as in some of the newer formations, the species are identical with those which now exist, the living type is only found within the torrid zone. A still more curious fact, is their identity in similar formations in different parts of the world. At the present day, the same soil in Pennsylvania and England produces plants of very different characters, and those which are native to each are of wholly distinct genera and species, while the fossils that accompany the coal in the two countries are precisely similar. But even those brought by Parry from the polar region of Melville island, are identical with those of England, and of course with those of this distant part of the same hemisphere in which the former are formed, although the character of the climate is so diverse. At the epoch of the coal formation, there existed plants, of genera, which, in temperate climates, at present rarely rise to more than a few inches in height, and which were at that remote period of enormous size. Thus, the forus must have attained the height of from fifty to sixty feet. At present, the forus assume the size of a tree only in the very warmest climates, and even there, are far inferior in magnitude to those of the coal formation. Now, it is well known, that the large size of the living species is due to great and constant heat, and copious moisture. Hence we may fairly infer that similar circumstances existed even at Melville island, where, at the present time, for the greater part of the year, the thermometer is below the freezing point.

As further instances of the same kind, we may quote the following facts. Faujas St. Fond found, in a marly slate, covered by lava, in France, the tree cotton, the liquid amber styrax, the cassia fistula, and other plants of tropical regions. The same observer found the fruit of the arcea palm near Cologne. The elastic bitumen of Derbyshire in England, is identical with the caoutchouc, which now grows only in the warmer parts of South America; and the amber of Prussia appears to be a fossil gum, similar to the Copal.

Among the more recent in formation of fossil vegetables, are the bituminized woods; these are often buried to great depths by diluvian action, but are never found in perfect rock. The most remarkable instance of this kind is at Bovey-Heathfield, in England, and beneath is found the retinasphaltum, that seems to be no more than the expressed viscorous juice of the trees. Coal is a similar formation, but due to a more ancient period. The mines of Pennsylvania occasionally furnish specimens, in which the fibre of the wood is as distinctly visible as in recently prepared charcoal. However these vast beds may have been formed, no doubt whatever can exist in respect to their vegetable origin.

Among animal remains found in the fossil state, shells and zoophytes are the most abundant. They form the principal parts of rocks which often occupy considerable districts. They are most frequent in calcareous strata, from the transition limestones to the highest of the marles. A remarkable fact is observed in respect to these shells, and the other fossils which accompany them; those which are found in the oldest, or transition formations, are more different from those that now exist, than those in the more modern deposits. Thus the transition limestones and slates contain terrebratulites, with encrinites, pentacrinites, and trilobites; in those of the submedial and medial series we find belemnites and the cornu ammonis; many of which are extinct genera, and some of which are of families that are no longer found living on our globe, while even where the genus is now to be met with, the species at least has become extinct; while in the latest of the tertiary or superior formations, we find ostracites, pectinites, buccinites, chamites, and many other genera that are still abundant, and even types of living species.

By far the greater part of the animals whose remains are found in the older strata are aquatic, and the vast extents over which they are distributed, show, that the waters must at one time have covered a very great proportion of what is now dry land. Nor has this change been produced by any gradual subsidence, for we find no coincidence in the levels of those portions of the land that contain similar fossils; some for instance are still lower than the level of the present ocean; others, again, of similar character, rest upon the tops or sides of the highest mountains. In Europe, the tops of the highest of the Pyrenees, rising 11000 feet above the level of the sea, are of limestone, containing numerous fossil remains, while Humboldt found a rock, similarly characterized, among the Andes, at the height of 14000 feet.

The ancient philosophers, who, in other departments of physical science, were far behind the moderns, seem in this alone to have pursued a process of inductive reasoning, which led to results far more accurate than any attained by the moderns, until within a very few years. The dogmatism which determined to find in every fossil aquatic remain a proof of the particular Noachic deluge, and the timidity of those whose researches had made them better informed, left the world wholly in the dark as to the real inferences to be drawn from a study of the structure of the earth; but what modern geologist could better express what are now admitted opinions, than the words which the Roman poet puts in the mouth of Pythagoras.