Chapter 14

We have stated that the zoophytes and shell-fish have left the most numerous fossil remains. Those of other families are not however rare. Fish, for instance, are found in great abundance, near Glarus in Switzerland, in clay slate; in Germany, at Papenheim, in a slaty marle, in the cupriferous slate of Eisleben, in the fetid limestone of Oehningen. They are also found in Egypt, and we have specimens of the same sort from Lyria, in a limestone apparently belonging to the oolitic or Jura formation. China and the coast of Coromandel have also fossils of this sort, but by far the greatest quantity have been procured from Mount Bolea, near Verona. A splendid suite from the last locality are to be seen in the Gibbs' Cabinet at New-Haven. Besides the impressions of entire fish, separate portions are very abundant, and perhaps the most frequent of these are the teeth of sharks, which are sometimes of a magnitude vastly greater than those of any living species. Animals of the class of amphibia appear not to have existed until after the aera that gave birth to fish. The oldest are probably the tortoises, of which a specimen has been found in sandstone near Berlingen. They have also been found in England, in the Netherlands near Brussels, at Aix in Provence, and in the quarries near Paris. The most remarkable fossils of this class belong, however, to the lizard family. Of these the most remarkable are the plesiosaurus, the megalosaurus, the iguanodon, and the crocodile of Maestricht, all belonging to extinct species.

The marine animals that are met with in a fossil state, are in great part foreign to the climates in which they are found buried. It has been shown that the fish of Bolea have their nearest living prototypes in the seas of Otaheite. The perpites of Gothland have been supposed to be petrifactions of the medusae of India. The madrepores, so abundant in Russia and in the frozen deserts of Siberia, only live now in seas within the tropics. Shells analogous to a great part of those found fossil in England, are only to be seen in the Atlantic, in a living state, on the coasts of Florida and Cuba. A shell-formed fossil at Havre is only to be met with recent at Amboyna.

Of the shells found in Italy, fossil in the sub Appenine hills, many are common to the Mediterranean and the Indian oceans. But while those in the fossil slate and the recent specimens from the tropics correspond in size, individuals of the same species from the Mediterranean are dwarfish and degenerate.

Thus then the remains of aquatic and amphibious animals appear to confirm the conclusion drawn from vegetable fossils, that a climate of temperature as elevated as that now found in the tropics, once extended into high northern latitudes. It has been seen that the fossil remains and impressions of shells have been found at great heights upon the sides, and even upon the tops of mountains; and that in the older of the strata no trace is to be found of any but aquatic animals. Thus before our existing mountains and the minerals they contain had arisen above the general surface; before diluvial and alluvial deposits, or even the great formations of sandstone and conglomerate had arisen from their disintegration, the globe was covered, in a great degree, and as it appears from considerations we have not space to enter into, by various successive eruptions, with waters, sometimes fresh, sometimes saline. These waters have, it could be readily made to appear, often rested long on the surface in a quiet state, after having been in violent agitation; and long ages of tranquillity have been succeeded and closed by convulsions of the most violent character.

In all the regularly stratified formations, animals of the mammiferous or cetaceous classes are wholly wanting; at least we have no proof that can be relied upon of any having been found in formations which took place prior to the last great deluge, that covered so much of the land with diluvium. In this last formation, however, they are often found in great abundance. Some of them are of recent, others of extinct species. Among the most remarkable of the latter are, the palaeotherium, and anoplotherium, found near Paris; the megalonyx, an animal of the sloth genus, but of the size of an ox, found in Virginia; a still larger sloth, called the megatherium, found near Buenos Ayres; the fossil elephant, as different from the living elephants of India or Africa, as the horse is from the ass, and which has been found in Europe, in Asia, and in America. The mastodon, of which several species have been discovered on the banks of the Hudson, in Kentucky, in Louisiana, in the plains of Quito, in France, and finally on the borders of the Irrawaddy.

The bones of rhinoceroses, bears, elephants, and hyaenas, have been found mixed in confusion in caverns; and it has been shown by Buckland that the latter animal had inhabited these caverns, and drawn thither the carcasses of the others as his prey, in one of the most perfect inductive arguments which has been produced, since Bacon propounded the rules of that species of reasoning.

"The moveable earths that fill the bottoms of valleys, and which cover the surface of great plains, have furnished us in the above two orders, of pachidermata and elephants, the bones of twelve species, to wit: one rhinoceros, two hippopotami, two tapirs, an elephant, and six mastodons. All these twelve species are now absolutely extinct in the climates in which their bones are found. The mastodons alone may be considered as forming a separate genus, now unknown, but closely approaching to the elephant. All the others belong to genera now existing in the torrid zone. Three of these living genera are now found only in the ancient continent, to wit: the rhinoceros, the hippopotami, and the elephant; the fourth, that of the tapirs, only exist in the new. The distribution of the fossil species is different; the tapirs have been found only upon the old continent, while elephants have been discovered in the new."

The fossil species, although belonging to known and existing _genera_, are essentially different in _species_ from those which now live upon the earth. The former are not mere varieties, but have marked specific differences. This at least is beyond all doubt in respect to the smaller of the hippopotami, and the gigantic tapir, as well as the fossil rhinoceros, and is extremely probable in respect to the elephant and the smaller tapir. If there be any question of the fact, it is only in respect to the greater hippopotamus.

"These different bones are buried in all different places in beds that resemble each other. They are often mixed indiscriminately with those of other animals, identical with those which exist at present. These beds are generally moveable, sandy, or marly, and always within a short distance of the surface. It is therefore probable that these bones have been enveloped by the last catastrophe of the globe. In a great number of places, they are accompanied by the accumulated spoils of marine animals; in other places, but these are less numerous, the remains of marine animals are not found, and sometimes the sand or marle that covers them contains only fresh-water shells. Although a small number of shells attached to fossil bones indicate that, they have remained some time under water, yet is there no authentic account of their having been found covered with regular stony beds, filled with marine remains, nor, in consequence, is there any proof of the sea having made a long and peaceable stay above them.

"The catastrophe that has covered them, would appear then to have been a great marine inundation, of no long duration, were it not that they are found upon the tops of high mountains, whither the waters of our present ocean could never have reached in their most violent agitations. On the other hand, these bones presenting no appearance of having been rolled, being occasionally only fractured, as the remains of our present domestic animals may occasionally be, and being sometimes found in entire skeletons, and accumulated as if in a common cemetery, demonstrate that the living beings to which they have belonged, must have met their fate in the very parts of the globe in which we now find the fossil monuments of their existence."

All the animals of which we have particularly spoken, are of genera now only found in the torrid zone, and the abundance of food which their great size would have caused them to require, renders their existence in numbers only possible in a warm climate. Their remains are, however, found in almost polar regions, whence we obtain a third link in the chain of evidence, that before the last great catastrophe to which the globe was subjected, its surface must have been warmer than at present.

We have seen in a former place, that such a change of temperature may have gradually occurred in consequence of a cooling of the external surface of the globe by an excess of its radiation above the quantity of heat received from the sun. The final cooling of its solid crust, down to the mean temperature at which we now find it, might, as is obvious, have been effected by a great irruption of waters, like that of which we have distinct evidence in the diluvial deposits, and the animal remains upon its surface. From that time, a state of equilibrium in the action of solar and terrestrial radiation having been attained, while the mean temperature still continues to depend upon the internal structure and nature of the globe, the distribution of heat upon the surface, and the vicissitudes of the seasons, have been solely influenced by the varying relation between these two radiations, which if equal to each other in their total amounts, differ in every different latitude, for every successive day in the year, and during each varying hour of the day.

It has been attempted to explain this change that has unquestionably taken place in the temperature of climate, by conceiving a change in the situation of the earth's axis. This hypothesis, however, is shown to be untenable by the calculations of physical astronomy: no other cause then remains but an actual change in the condition of the earth itself.

The most remarkable of all the phenomena which the earth presents, are the great changes of weight that have taken place in identical formations which must have arisen from the prevalence of water, and therefore nearly if not exactly upon the same level. The primitive or lowest stratified rocks, probably had not water for their cause; still, however, they must have been in the fluid state, and these are not only found beneath all other rocks, and in the lowest places to which the industry of man has penetrated, but they also rise and form the greatest part in bulk of many of the highest mountains; indeed, if we except volcanic mountains, of all the more elevated masses. The transition and secondary formations are subject to similar although less changes of level, rising, as has been seen, to the tops of the Pyrenees, and to even a greater height on the sides of the Andes. The tertiary or superior formations are found in Italy and Sicily, forming mountains several thousand feet in height, while the latest of all, the diluvial with its embedded mammalia, exists in the lofty table land of Quito. The inference is irresistible, that we do not now find these deposits at the levels where they were left by the ocean, as in the case of the primitive rocks by their own crystallization from a fluid state, but that they have been altered in their positions by actions of a character totally distinct from that by which they were originally formed.

This inference is still further confirmed by the great and sudden changes of level that are frequently to be seen in similar strata, faults, as they are styled by miners, in which the same bed has its level sometimes changed hundreds, nay even thousands of feet. These faults, if in greatest abundance in the more ancient rocks, are to be found even in the newest, and sometimes affect several formations incumbent on each other, of ages the most different. Thus, then, we have distinct and conclusive evidence, that as we inferred from theory, the solid crust of the globe has been shattered and fractured repeatedly, and at all the different epochs of its history. This fracturing and cracking we have shown, must, in conformity with strict mechanical laws, have been attended with the rise of the molten liquid from beneath, which ought in some cases to have formed veins and dykes, in the places where the fractures occurred. It is however possible, that the rise of the fluid from beneath, may not have taken place where the pressure occurred; but it would then have been compelled by hydrostatic pressure, to issue at some other point, breaking and tearing the weaker parts of the solid crust, in order to afford itself a vent.

The latter class of phenomena are still in action, and we have evident traces of their occurrence in all the different stages of the world's existence; of the former it will also be seen there is conclusive evidence.

The visible effects of a subterranean heat, are most frequently met with at the present day in the form of volcanoes. Of these, there are not only a great number in activity, but there are still more that have been certainly active since the last great change that the surface of the earth has undergone.

That part of the great group of mountains which we have before described, which lies in the new continent, contains many active volcanoes, and others but recently extinct. Terra del Fuego, as its very name imports, is the seat of many; Chili has several; in Peru are to be noted Arequipa, Pichinca, and Cotapaxi; while Chimborazo is obviously one that has become extinct at a period not remote. Passing the Isthmus of Panama, we find the volcanoes of Guatimala and Nicaragua almost infinite in number. In Mexico, are Orezaba, Popocatepetl, and Jorullo; the last of which first rose from beneath the surface in 1759. California has five active volcanoes; and we know, from the observations of La Perouse and Cook, that they also exist along the north-western coast of America. Mount St. Elias, in particular, was seen in a state of eruption. These mountains connect those of Mexico with the volcanoes of the Aleutian islands and of the peninsula of Alaska, which continue the system towards Kamtschatka, in which peninsula there are three of great violence. We have seen some proofs, that there are active volcanoes to the north-west of China, but none now exist in Thibet; and the action that once took place there has sought new vents, in regions more near to the present bed of the ocean. Thus, Japan has eight volcanoes, Formosa several, and, in proceeding to the south, the land of volcanic action widens, and becomes of immense extent. It embraces the Philippine, Marian, and Molucca islands, Java, Sumatra, Queen Charlotte's islands, and the New-Hebrides. The active volcanoes of Europe and western Asia are few in number; but those that are extinct form a great system, in which the active ones are included, and which seems to spread in the form of a belt, from the Caspian sea to the Atlantic. Volcanic action still occurs on the shores of the Caspian. In the chain of Elburg is a lofty mountain that still emits smoke, and around whose base are several distinct craters. Syria and Palestine abound in volcanic appearances, of which the great crater that has swallowed up the waters of the Jordan, and forms the Dead sea, is the most remarkable. Greece and the Grecian Archipelago have been, almost within historic times, the seat of a volcanic action, of great extent and violence, and which has not wholly exhausted itself. In Sicily, AEtna has burnt for 3300 years, and is yet surrounded by extinct craters of more ancient date. The Lipari islands are wholly volcanic. Vesuvius, that had long before intermitted its eruptions, and broke forth again in the great one that destroyed Herculaneum and Pompeii, is not the only volcanic mountain of Naples. An extinct one of much greater size is to be found near Roccafina. The catacombs of Rome are excavated in lava, and Tuscany contains strong evidences of volcanic action. Volcanic indications can be traced near Padua, Verona, and Vicenza, extending into Dalmatia. A district of Hungary was suspected of containing the seeds of subterranean fire, and the suspicion has been confirmed by an actual eruption. Germany and Bohemia contain a great number of extinct volcanoes, as does the south of France, and particularly Auvergne. In Spain, too, the proofs of a volcanic agency are clear and decisive.

Greenland and Iceland present a third group of volcanoes; in the latter island, a single volcano was in a state of continuous eruption for five or six years. The Azores, the Canaries and Madeiras, also contain numerous volcanoes, both active and extinct, as do the Caribbean islands.

In comparing together volcanoes that are in present activity, and others in which the crater and the streams of emitted lava are too distinct to permit a doubt of their having arisen from the same cause, differences are observed that only have arisen from great differences in the circumstances under which the eruption has taken place. In many of the ancient volcanoes, we find the emitted streams are arranged in prismatic forms, constituting basalt, and frequently passing into what under other circumstances would be styled _trap_ by the Wernerians. Now, we know that when streams of lava enter the sea, they spontaneously assume the prismatic structure. Hence we may infer, that these ancient volcanoes originally gave vent to their craters beneath the level of the sea, at a time when the rocks through which they penetrated, and over which their streams have passed, were beds of the primitive ocean. The trap rocks themselves may have been formed in a similar manner, by upward pressure of the igneous fluid beneath, through the veins and fissures formed on the breaking of the solid crust. Trap traverses, in dykes of unknown depth, many formations, and is occasionally seen forming beds between successive strata. It frequently occurs in faults, and sometimes in extensive overlying masses. Close observation, and a just course of analogy, lead to the irresistible conclusion, that all the trap rocks, however situated or arranged, grow out of the same great cause, the rising of the liquid interior of the earth to its surface. An action sometimes taking place through veins and fissures in the solid crust, and sometimes by the eruption of volcanoes, both occurring during the pressure of water upon the surface. One of the most extensive groups of trap-rocks is to be seen in the north-eastern part of the state of New-Jersey. The Hudson is bordered for nearly forty miles by a great ridge of columnar rock, lying upon sandstone. When this is surveyed with an eye to its analogy to volcanic action, it appears as if it were the outpourings of a crater, whose basin is now occupied by the lake in which the Hackensack river takes its rise, and whence a great stream of lava has run over the sandstone rock, as far as the strait that separates Staten Island from the main land. The two Newark mountains are ridges of the same description, of even greater extent; other smaller ridges of the same kind are also distinctly visible, and the whole of this last system appears to have proceeded from a crater now filled by the alluvion of the Passaic, but which is bordered by a ridge still occupying two-thirds of a circle, and showing conclusive marks of igneous action, that goes by the name of the Hook mountain. The phenomenon of a dyke of trap is well exhibited in the quarries near Hartford in Connecticut, where this rock has been laid bare for a considerable depth, as it rises through a sandstone rock, instead of overlying it, as it is seen to do on the Hudson.

The trap-rocks, which are, generally speaking, of the character called by mineralogists greenstone, vary in this district of New-Jersey, from a compact basalt of homogeneous structure, to one of regular and distinct crystallization, not distinguishable in hand specimens from primitive syenite. A rock of this last character is to be found in the mountain that extends from Morristown to Mount Kemble, which is columnar in its structure, but almost identical, in mere external characters, with stratified rocks of gneiss containing hornblende, that are found in the primitive ridges within a few miles.

Thus then the older volcanic rocks gradually pass in character into those which, under the general name of granitic, form the apparent nucleus of gneiss and mica slate mountains, and penetrate them, and the primitive limestones, in veins. One of the best instances of veins of granite with which we are acquainted, are those which occur in the quarries of white marble at Kingsbridge, which are traversed in every direction by thin veins of a rock, principally composed of a white fetid felspar, mixed with spangles of silvery mica, and small grains of quartz, interspersed with occasional masses of tourmaline. The famous locality of chrysoberyl, beryl, and other interesting minerals, at Haddam, in Connecticut, is said to occur in a granitic vein passing through strata of gneiss.

In all these cases we cannot fail to see evidence of igneous eruptions, taking place, however, under circumstances widely different from those of our present terrestrial volcanoes, or of the submarine craters of more remote dates, but which can be readily explained by supposing, either that the penetration took place when the surface of the earth was so intensely heated as to admit of the injected veins being slowly cooled, and therefore more perfectly crystallized; or that the issuing mass was so great as to retain its heat for a great length of time.

It might at first sight appear difficult to explain how volcanic energies should still continue in activity, now that the mean temperature of the earth has become constant, and the outer crust can be no longer subject to the shrinking, and consequent cracking which it must have undergone while cooling. The phenomena that attend volcanic eruptions furnish a full explanation of this, for they are attended in almost all cases with the evolution of great quantities of gaseous matters, and steam, which must therefore exist in a state of intense compression, and at elevated temperatures, in the mass whence the volcanic flood issues. Their elastic energies are sufficient to account for all the striking effects that attend the action of volcanoes.

The earthquake is a phenomenon connected with volcanic eruptions, and arising from the same great cause; but while the latter are confined to certain mountains, and restricted within narrow limits at the present day, an earthquake is sometimes found to prevail over a very large portion of the earth's surface. To omit the more usual phenomena of earthquakes, we shall speak of but one, which has in some cases been observed, that throws a great light upon the manner in which the stratified rocks have had their levels changed, and been dislocated and distorted in the manner we now find them. We allude to the sudden raising of countries of greater or less extent. Of this we shall quote three several instances from a paper of Arago's.