Part 4 (2/2)

The phenomenon of raised sea-beaches is one of great interest, and seems to be connected with the alternate elevations and depressions of the Tertiary epoch, perhaps marking the successive steps of the upheaval of the land. In several parts of England the coast-line exhibits one or more shelves parallel with the existing sea-beach, and covered with similar s.h.i.+ngle, sand, and sea-sh.e.l.ls. And the same phenomenon is exhibited on a still more gigantic scale in South America. Mr.

Darwin[39] found that for a distance of at least 1,200 miles from the Rio de la Plata to the Straits of Magellan on the eastern side, and for a still longer distance on the west, the coast-line and the interior have been raised to a height of not less than 100 feet in the northern part, but as much as 400 feet in Patagonia. All this change has taken place within a comparatively short period; for in Valparaiso, where the effect is most considerable, modern marine deposits, with human remains, are seen at the height of 1,300 feet above the sea.

At what exact point, geologically, the period of human history begins, it is impossible to say. No evidence of Man's presence has occurred older than the latest Tertiary deposits, which insensibly merge into the Alluvial. It seems certain that human remains have been found in chronological a.s.sociation with those of animals long extinct, and there appears no reason to doubt that some species of animals, as the Irish Deer, the Moa of New Zealand, and the Dodo of the Mauritius, have disappeared from creation within a period of a few centuries.[40] It is not improbable that the last of the Moho race may have lived only long enough to grace the pages of the ”Birds of Australia.”

[Ill.u.s.tration: THE MOHO.]

It is as important as it is interesting, to observe that the same kinds of physical operations have been, within the present epoch, and are still, going on, as those whose results are chronicled in the rocks.

Strata of alluvium are constantly being formed on a scale which, though it does not _suddenly_ affect the outline of coasts, and therefore appears small, yet is great in reality.

The Ganges is estimated to pour into the Indian Ocean nearly 6,400 millions of tons of mud every year; and its delta is a triangle whose sides are two hundred miles long. The delta of the Mississippi is of about the same size, and it advances steadily into the Gulf of Mexico at the rate of a mile in a century.

The acc.u.mulation of river-mud is gradually filling up the Adriatic Sea.

From the northernmost point of the Gulf of Trieste to the south of Ravenna, there is an uninterrupted series of recent accessions of land, more than a hundred miles in length, which, within the last twenty centuries, have increased from two to twenty miles in breadth.

The coral-polypes are working still with great energy. Mr. Darwin mentions two or three examples of the rate of increase, one of which only I shall cite. In the lagoon of Keeling Atoll, a channel was dug for the pa.s.sage of a schooner built upon the island, through the reef into the sea; in ten years afterward, when it was examined, it was found almost choked up with living coral.

Volcanic action is busy in many parts of the earth, pouring forth clouds of ashes and torrents of molten rock; and instances are not wanting in which new islands have been raised from the bed of the ocean by this means, within the sphere of history.

Slow and permanent changes of level are still being produced on the earth's crust. The bottom of the Baltic has been, for several centuries at least, in process of continuous elevation, the effects of which are palpable. Many rocks formerly covered are now permanently exposed; channels between islets, formerly used, are now closed up, and beds of marine sh.e.l.ls have become bare. On the other hand, the whole area of the Pacific Polynesia seems subsiding.

Deposits are being made by waters which hold earthy substances in solution. The princ.i.p.al of these is _lime_. Several remarkable examples of this kind are quoted by Sir Charles Lyell, in one of which there is a thickness of 200 or 300 feet of travertine of recent deposit, while in another a solid ma.s.s thirty feet thick was deposited in about twenty years. He also states that there are other countless places in Italy where the constant formation of limestone may be seen, while the same may be said of Auvergne and other volcanic districts. In the Azores, Iceland, and elsewhere, _silica_ is deposited often to a considerable extent. Deposits of _asphalt_ and other bituminous products occur in other places.[41]

The floors of limestone caverns are frequently strewn with fossil bones, which are imbedded in stalagmite, and this incrustation is still in progress of formation. It is remarkable that in this deposit alone we obtain the bones of Man in a fossil condition. The two creations,--the extinct and the extant,--or rather the prochronic and the diachronic--here unite. But there is no line of demarcation between them; they merge insensibly into each other. The bones of Man, and even his implements and fragments of pottery, are found mingled with the skeletons of extinct animals in the caves of Devons.h.i.+re, in those of Brazil,[42] and in those of Franconia. In Peru, some scores of human skeletons have been found in a bed of travertine, a.s.sociated with marine sh.e.l.ls; the stratum itself being covered by a deep layer of vegetable soil, forming the face of a hill crowned with large trees.

From a very interesting paper by M. Marcel de Serres, it appears indubitable that the existing sh.e.l.ls of the Mediterranean are even now pa.s.sing in numbers into the fossil state, and that not in quiet spots only, but where the sea is subject to violent agitations. Specimens of common species, ”completely petrified, have been converted into carbonate of lime at the same time that they have lost the animal matter which they originally contained. Their hardness and solidity are greater than those of some petrified species from tertiary formations.”

”In the collection of M. Doumet, Mayor of Cette, there exists an anchor which exhibits the same circ.u.mstances, and which is also covered with a layer of solid calcareous matter. This contains specimens of _Pecten_, _Cardium_, and _Ostrea_, completely petrified, and the hardness of which is equal to that of fossil species from secondary formations. On the surface of the deposit in which the anchor is imbedded, there are _Anomiae_ and _Serpulae_, which were living when the anchor was got out of the sea; these present no trace of alteration.”[43]

Thus we have brought down the record to an era embraced by human history, and even to individual experience; and we confidently ask, Is it possible, is it imaginable, that the whole of the phenomena which occur below the diluvial deposits can have been produced within six days, or seventeen centuries? Let us recapitulate the princ.i.p.al facts.

1. The crust of the earth is composed of many layers, placed one on another in regular order. All of these are solid, and most are of great density and hardness. Most of them are of vast thickness, the aggregate not being less than from seven to ten miles.

2. The earlier of these were made and consolidated before the newer were formed; for in several cases, it is demonstrable that the latter were made out of the _debris_ of the former. Thus the compact and hard granite was disintegrated grain by grain; the component granules were rolled awhile in the sea till their angles were rubbed down; they were slowly deposited, and then consolidated in layers.

3. A similar process goes on again and again to form other strata, all occupying long time, and all presupposing the earlier ones.[44]

4. After some strata have been formed and solidified, convulsions force them upward, contort them, break them, split them asunder. Melted matter is driven through the outlets, fills the veins, spreads over the surface, settles into the hollows, cools and solidifies.

5. After the outflowing and consolidation of these volcanic streams, the action of running water cuts them down, cleaving beds of immense depth through their substance. Mr. Poulett Scrope, speaking of the solidified streams of basalt, in the volcanic district of Southern France, observes:--

”These ancient currents have since been corroded by rivers, which have worn through a ma.s.s of 150 feet in height, and formed a channel even in the granite rocks beneath, since the lava first flowed into the valley. In another spot, a bed of basalt, 160 feet high, has been cut through by a mountain stream. The vast excavations effected by the erosive power of currents along the valleys which feed the Ardeche, since their invasion by lava-currents, prove that even the most recent of these volcanic eruptions belong to an era incalculably remote.”[45]

6. A series of organic beings appears, lives, generates, dies; lives, generates, dies; for thousands and thousands of successive generations.

Tiny polypes gradually build up gigantic ma.s.ses of coral,--mountains and reefs--microscopic foraminifera acc.u.mulate strata of calcareous sand; still more minute infusoria--forty millions to the inch--make slates, many yards thick, of their sh.e.l.ls alone.

7. The species at length die out--a process which we have no data to measure,[46] though we may reasonably conclude it very long. Sometimes the whole existing fauna seems to have come to a sudden violent end; at others, the species die out one by one. In the former case suddenly, in the latter progressively, new creatures supply the place of the old. Not only do species change; the very genera change, and change again. Forms of beings, strange beings, beings of uncouth shape, of mighty ferocity and power, of gigantic dimensions, come in, run their specific race, propagate their kinds generation after generation,--and at length die out and disappear; to be replaced by other species, each approaching nearer and nearer to familiar forms.

8. Though these early creatures were unparalleled by anything existing now, yet they were animals of like structure and economy essentially. We can determine their a.n.a.logies and affinities; appoint them their proper places in the orderly plan of nature, and show how beautifully they fill hiatuses therein. They had sh.e.l.ls, crusts, plates, bones, horns, teeth, exactly corresponding in structure and function to those of recent animals. In some cases we find the young with its milk-teeth by the side of its dam with well-worn grinders. The fossil excrement is seen not only dropped, but even in the alimentary ca.n.a.l. Bones bear the marks of gnawing teeth that dragged them and cracked them, and fed upon them. The foot-prints of birds and frogs, of crabs and worms, are imprinted in the soil, like the faithful impression of a seal.[47]

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