Part 9

Per-centage No. of Periods. Localities. of fossils recent. compared.

Eocene {London and Hampshire } 1 or 2 400 Miocene {Red and Coralline } 20 to 30 450 { Crag, Suffolk } Older Pleiocene {Mamaliferous or Norwich } 60 to 70 111 { Crag } Newer Pleiocene {Marine strata near } 85 to 90 160 { Glasgow } Post Pleiocene {Fresh-water of the valley} 99 to 100 40 { of the Thames }

It is to this period that are assigned the animals whose bones are found in astonishing numbers in limestone caverns, as, for example, that notable one at Kirkdale, in Yorkshire, which was examined by Professor Buckland.

This is a cave in the Oolitic limestone, with a nearly level floor, which was covered with a deposit of mud, on which an irregular layer of sparry stalagmite had formed by the dripping of water from the low roof, carrying lime in solution. Beneath this crust the remains were found.

Of the animals to which the bones belonged, six were Carnivora, viz. hyaena, felis, bear, wolf, fox, weasel; four Pachydermata, viz. elephant, rhinoceros, hippopotamus, horse; four Ruminantia, viz. ox, and three species of deer; four Rodentia, viz. hare, rabbit, water-rat, mouse; five Birds, viz. raven, pigeon, lark, duck, snipe.

The bones were almost universally broken; the fragments exhibited no marks of rolling in the water, but a few were corroded; some were worn and polished on the convex surface; many indented, as by the canine teeth of carnivorous animals. In the cave the peculiar excrement of hyaenas (album graecum) was common; the remains of these predacious beasts were the most abundant of all the bones; their teeth were found in every condition, from the milk-tooth to the old worn stump; and from the whole evidence Dr. Buckland adopted the conclusion, in which almost every subsequent writer has acquiesced, that Kirkdale Cave was a den of hyaenas during the period when elephants and hippopotami (not of existing species) lived in the northern regions of the globe, and that they dragged into it for food the bodies of animals which frequented the vicinity.

Thus in these spots we find, observes Professor Ansted, "written in no obscure language, a portion of the early history of our island after it had acquired its present form, while it was clothed with vegetation, and when its plains and forests were peopled by many of the species which still exist there; but when there also dwelt upon it large carnivorous animals, prowling about the forests by night, and retiring by day to these natural dens."

In our own country, and in many other parts of the world, we find fragments of stone distributed over the surface, sometimes in the form of enormous blocks, bearing in their fresh angles evidence that they have been little disturbed since their disruption, but sometimes much rubbed and worn, and broken into smaller pieces, till they form what is known as gravel. In many cases the original rock from which these masses have been separated does not exist in the vicinity of their locality; and it is not till we reach a distance, often of hundreds of miles, that we find the formation of which they are a component part.

Various causes have been suggested for the transport of these erratic blocks, of which the most satisfactory is the agency of ice, either as slow-moving glaciers, or as oceanic icebergs.

"The common form of a glacier," says Professor J. Forbes, "is a river of ice filling a valley, and pouring down its mass into other valleys yet lower. It is not a frozen ocean, but a frozen torrent. Its origin or fountain is in the ramifications of the higher valleys and gorges, which descend amongst the mountains perpetually snow-clad. But what gives to a glacier its most peculiar and characteristic feature is, that it does not belong exclusively or necessarily to the snowy region already mentioned. The snow disappears from its surface in summer as regularly as from that of the rocks which sustain its mass. It is the prolongation or outlet of the winter-world above; its gelid mass is protruded into the midst of warm and pine-clad slopes and green-sward, and sometimes reaches even to the borders of cultivation."

The glacier moves onward with a slow but steady march towards the mouth of its valley. Its lowest stratum carries with it numerous fragments of rock, which, pressed by the weight of the mighty mass, scratch and indent the surfaces over which they move, and sometimes polish them. These marks are seen on many rock-surfaces now exposed, and they are difficult to explain on any other hypothesis than that of glacial action.

But the alternate influence of summer and winter--the percolation of rain into the mountain fissures, and the expansion of freezing--dislodge great angular fragments of rock, which fall on the glacier beneath. Slowly but surely these then ride away towards the mouth of the valley, till they reach a point where the warmth of the climate does not permit the ice to proceed; the blocks then are deposited as the mass melts. But if the climate itself were elevated, or if the surface were lowered so as to immerse the glacier in the sea, it would melt throughout its course, and then the blocks would be found arranged in long lines or moraines, such as we see now in many places.

If the glacier-valley debouch on the sea, the ice gradually projects more and more, until the motions of the waves break off a great mass, which floats away, carrying on its surface the accumulation of boulders, gravel, and other debris which it had acquired during its formation. It is now an iceberg, which, carried by the southern currents, approaches a warmer climate, melts, and deposits its cargo, perhaps hundreds of leagues from the valley where it was shipped, and as fresh as when its component frusta were detached from the primitive rock.

If the abundance of such erratic blocks and foreign gravel seem to require a greater amount of glacial action than is now extant, it has been suggested that the volcanic energy which elevated Europe may have been succeeded by a measure of subsidence before the land attained its present permanent condition. Hence there may have been, during the Tertiary epoch, mountain chains of great elevation, sufficient to supply the glaciers, which, on their subsidence, melted on the spot where they were submerged, or floated away as icebergs on the pelagic currents, till they grounded on the bays and inlets of other shores, which were subsequently elevated again.

Thus a large portion of the animals which then inhabited these islands (up to that time, perhaps, united to the continent) would be drowned, and many species quite obliterated, a few alone remaining to connect our present fauna with that of the submerged area, when the land rose again to its existent state.

It would not materially augment the force of the evidence already adduced on the question of chronology, to examine in detail the fossil remains of South America, Australia, and New Zealand. The gigantic Sloths of the first, the gigantic Marsupials of the second, and the gigantic Birds of the third, however interesting individually, and especially as showing that a prevailing type governed the fauna in each locality then as now--are all formations of the Tertiary period, and some of them, at least, seem to have run on even into the present epoch. Indeed, it is not quite certain that the enormous birds of New Zealand and Madagascar are even yet extinct.

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 shingle, sand, and sea-shells. And the same phenomenon is exhibited on a still more gigantic scale in South America. Mr. Darwin 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 association 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. 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."

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 accumulation 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 passage 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 shells 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 principal 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 mass 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.

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 Devonshire, in those of Brazil, and in those of Franconia. In Peru, some scores of human skeletons have been found in a bed of travertine, associated with marine shells; 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 shells of the Mediterranean are even now passing 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 circumstances, 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."