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like. Reptiles are also found similar to those in the Wealden. Bones of birds have been discovered, as also bones of what seems to be a species of monkey.

Scenery.—The Chalk series appears to be wholly a marine deposit. The land we know little or nothing of; sufficient, however, to shew that it was clothed with vegetable life, as in other periods, but little to picture its appearance. Over it, huge Wealden reptiles sought their prey, birds flew, and great apes swung from tree to tree. But the ocean swarmed with varied life, mild sea-breezes blew, and smiling sunbeams sparkled upon its waters; for the climate was warm, as shewn by the corals, reptiles, and monkeys. In the tepid waters lived numberless fishes and shells, and on their surface the nautilus spread its coloured sail.

The origin of chalk is a problem not yet satisfactorily settled, but the generally received opinion is, that the shores were fringed by coral reefs, which the dashing waves gradually wore down into fine powder, as they still do in tropical seas, while millions of shell-fish teemed in its waters, and left their white shells as an impalpable sand, that, under the microscope, shews the tiny houses of the old inhabitants as perfect as on the day they died. Flint seems mostly to consist of concretions round sponges, corals, and other substances, and may be found at any epoch, and occurs in many other formations besides the Chalk, though there in greatest abundance.

XI.-Tertiary System.

We have now arrived at a new epoch in the history of the rocks, known as the Epoch of Recent Life. Henceforward, the plants and animals bear not only a close resemblance to those now existing, but a great proportion of them are identical. We discover real exogenous trees, the same corals, crustaceans, and shells, equal-lobed fishes, birds, and mammals of existing families—and all these not only more numerous than hitherto, but also more perfectly preserved. The name given to this system is a relic of the names used in early geology, when all rocks were divided into Primary, Secondary, and Tertiary. In the Tertiary System, two great periods are easily distinguishable: 1. The Warm Period; 2. The Cold Period.

1. THE WARM TERTIARY PERIOD.—This system exhibits clays, sands loose or hard, gypsum or plaster of Paris, and marls. The only true rock is limestone, made up of innumerable little shells, so numerous that the stone, which is extensively found throughout the world, is named from its coin-like shells, nummulitic.1 The limestone is burned for various purposes; the clays are extensively used; the harder sands are employed for

1 From Latin nummus, a coin.

building; and amber is also found. The strata occur exclusively in patches known as basins, the London and Paris basins being the most important.

Fossil Remains. The remains are both numerous and important. Of plants, there are few marine specimens, as these were too tender to be preserved. We find, however, mosses, palms, ferns, leaves, fruits, seeds of different kinds, and whole pods of pea-plants.

We have real

exogenous timber, with specimens of fine palm, cypress, and fir.

The animals resemble or are identical with existing species, and the Tertiary System has been divided into periods according to the percentage of life-remains. We have corals, star-fish of the same species as those existing, and the shells are very beautiful, finely preserved, and scarcely distinguishable from those to be gathered on our present shores.

Among the fishes, we find various species of the shark, ray, sturgeon, sword-fish; and of fresh-water kinds, the perch and the carp. Among the reptiles there are the crocodile and alligator, and the turtle. Birds are numerous, one specimen found in the Paris basin being gigantic. Mammals are found of every existing order, amongst others the whale, elk, stag, antelope, camel, lama, tapir, hog, rhinoceros, hippopotamus, beaver, hare, squirrel, monkey, elephant, horse, tiger, and hundreds of others. So numerous are these remains in some parts, that one rock in Norfolk is known as the Mammaliferous Crag. But the most remarkable of the ancient animals are the huge monsters whose skeletons, carefully reconstructed, may be seen in the British Museum, some of them above 10 feet

high, and 20 feet long. The most wonderful is the mammoth, with two great tusks like an elephant. Others are the dinotherium or 'fierce wild beast,' the megatherium2 or 'great wild beast,' and the mastodon. In different parts of the world, and in many places in England, remarkable caves are found filled with bones of various animals in clay or sands, known as 'bone-caves.' These caves have some of them been the dens of savage tigers and other brutes, the bones of their prey being still found; some the abodes of different creatures at different times who have lived and died there; while others have had their contents washed into them by floods.

Fig. 93.-Dinotherium.

Scenery. During this period shallow seas rolled under a genial sun, in

1 From Greek deinos, terrible, and therion, beast.

2 From Greek megas, great, and therion, beast.

which low islands rose crowned with palms, while the savage shark and sword-fish swam in the surrounding waters; the elephant ranged through the tall groves on shore; the hippopotamus wallowed in the fresh-water lakes; the rhinoceros crashed through rank jungles; the mastodon, mammoth, and tapir trod in forests of palm; and the wild ox and buffalo roamed over wide grassy prairies.

2. THE COLD TERTIARY PERIOD.-Immediately above the strata just described, with these strange organisms that speak of a warm climate, are found remarkable accumulations of sand, often found pure in hillocks; gravel, and clay interspersed with rounded worn boulders, known under

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the general title of the 'Boulder Clay,' some of the boulders being of enormous size. From various phenomena, as shewn in a former chapter, it has been proved that the climate became arctic in character, and our country and others enveloped from shore to shore in a vast ice-sheet, like the Greenland of to-day. From the ends of this huge ice mantle, immense masses broke off and floated away as icebergs. By and by, however, the

climate became milder, and Britain looked like Norway and Iceland, with glaciers on the higher grounds, reaching here and there to the sea.

Gradually the great ice-fields melted away under the rays of the genial sun, and our country looked like the present Switzerland, till at length the last glacier disappeared from the highest hills. The effects of all the wear and movement of these ice-masses, whether grinding down the land or grating on the floor of the ocean, or dashing against opposing islands, are seen in the thick clay and sand deposits everywhere around us, enclosing worn stones and gravel; the scratched and rounded rock-surfaces often bright and smooth as polished marble; the 'erratic boulders,' perched on our hill-tops and plains; and the general wavy outline of all higher ground throughout our land. This glaciation has been ascertained to extend over the whole of Northern Europe and America, and round the shores of the Antarctic Ocean.

XII. Quaternary or Recent Period.

We have now reached the last of the great geological epochs, during which sea and land, plants and animals, have remained little changed from what they are now. This last system has been variously named the Post Tertiary, Quaternary, or Recent.

The whole system may be divided into two chief periods:

1. The Prehistoric, or that before history was written.

2. The Historic, or that since history was written.

During the whole epoch, there is little or no solid rock, the whole deposits consisting of clay, sand, gravel, mud, peat, and the like.

Of prehistoric deposits, we find such remains as these: plants of all kinds, all common shells and corals, and common animals, with a few now extinct, such as the long-fronted ox, the gigantic Irish deer—a creature ten feet high to the top of its horns-the elephant, rhinoceros, hyena, bear, and mammoth, besides human remains in bones, canoes, ashes, dwellings, and weapons.

In historical times, we find similar remains, but the deposits are comparatively small; and the plant and animal remains are almost solely those now existing in each country. Men have left traces of themselves in buildings, coins, implements, weapons, and works of art; while peatbogs have been formed, forests have been submerged or cut down, and considerable changes in sea-level have taken place.

Since the glacial epoch, a continuous series of changes has been going on without intermission, accomplished by various causes and in various ways. The land has changed its level several times both by elevation and depression, the sea thus alternately encroaching on and retiring from the land. Whole countries have been gained from the ocean, such as the Fens

in England and the greater part of Holland; old beaches may be distinctly traced, with their cliffs, shores, and shells far above sea-level; whole forests have been submerged, whose old trunks and fruits are thrown up by every storm; and huge accumulations of sand, blown or washed, have been found along its shores. Rivers have been depositing new matter under the ocean at their mouths, increasing the land by the formation of deltas, sometimes hundreds of miles in extent, laying down fine carse-land along their banks, that now forms the richest soil of the farmer, and leaving terraces far above their present level, to mark their former beds. Many lakes have been formed, others are gradually silting up from the earthy matter brought down by rivers, while some have become quite dry and are now waving with corn. Animals have been busy forming new islands and continents, as in the Pacific, where the coral insect leaves its skeleton to form the nucleus of future islands; birds have deposited guano; and myriads of microscopic creatures cover the floor of the ocean, some of the earths now existing being so full of these as to be used by savage tribes as food; and igneous agencies have been and are as active as in the olden times in changing the land and throwing out vast deposits of lava and ashes.

Man.—It is an interesting question how far back man extends into these geologic eras, and this important inquiry has of late years received great attention. Striking results have also been arrived at. It seems to be indisputably proved that man existed as far back as the great glacial period, at the close of the Tertiary epoch, and that he was contemporary with the hairy rhinoceros, mammoth, woolly elephants, and other gigantic creatures now long extinct, which he no doubt hunted as he now does the fox and the deer; and at a period when Britain was united to France, where now the sea flows in the Straits of Dover, his bones have been found in the same deposits with these animals. But this subject is but in its infancy, and it would therefore be unwise to make positive statements where our data are insufficient. Enough has, however, been discovered to shew that men have lived with strange denizens for many ages, and under very different conditions, in our own quiet land.

Fig. 95.-Encrinite.

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