THE MESOZOIC SYSTEM—THE TRIASSIC, OOLITIC, AND CRETACEOUS FORMATIONS—THE EOCENE, MIOCENE, AND PLIOCENE—THE GLACIAL PERIOD—PRE-HISTORIC MAN.

We trust that the general reader has gleaned from the foregoing chapter some few ideas concerning the growth of plant and animal life in the early periods of the world’s existence. From the Laurentian System we have briefly traced the conformation of the globe at the dawn of organic life through the Silurian Old Red Sandstone and Carboniferous formations, indicating as we proceeded the chief points in the world’s history, and the gradual development of life through many ages. There is no real or bold line of demarcation drawn between these systems. As seam unites to seam, and layer to layer, stratum upon stratum, so the systems almost insensibly unite, and forms of life appear, mature, and die away as the babe grows into the man, and dies away again to old age and final extinction. So one system merges into another, each and all a factor in the great work which was intended to prepare the earth for the greatest and latest development of Nature—Man!

But all this while the earth had been, as it still is, undergoing continual change. Sometimes gradually, in the wearing away, or elevation of beach or headland; sometimes suddenly, as when mighty hills were upheaved and the deeply-laid granite or limestone was lifted to the summits of the mountains from the depths of the sea. Land and water came and went, and the ever-changing earth still brought forth abundantly “the herb yielding seed after its kind,” and the “moving things upon the ground after their kind,” ever improving and developing till they culminated in the splendid vegetation and immense animals of the Tertiary period, and lay silent afterwards in the cold grasp of the great ice age for the thousands of years of the glacial epoch.

We now enter upon the Trias, or New (Upper) Red Sandstone, which is divided into Upper and Lower Trias, “Keuper” and “Bunter.” We have three principal headings in the Secondary System—the Triassic (the oldest), the Oolitic, and the Cretaceous. In the first we find red sandstones and shelly limestone; in the second, clays and shale; in the last, chalk, or white limestone. In some districts there are traces of volcanic action.

On the top of the “Upper Trias,” or “Keuper” formation, we have the Lias, which succeeds the RhÆtic beds, and in this we find many rich traces of reptiles and birds which come now before us in the rising scale of creation. In the seas of this period we have numerous crustacea, the nautilus and the cuttle-fish. The Saurians now come before our retrospective vision. It is the “Reptile Age” in all its development, and the huge labyrinthodon, the iguanodon, pterodactyle, and ichthyosaurus testify to the magnitude of the fauna of the period. The first mammal specimen, a marsupial, has been traced back to this time; and the tropical temperature was favourable for luxuriant vegetation, pines, and palms.

In the swamps or shallow waters the great reptiles disported themselves, and seized their prey, the water-fowl, which now appeared in numbers, and of enormous size. Nor were insects absent. Numbers of remains have been discovered; beetles, dragon-flies, grasshoppers, etc., in multitudes yield us information, while the marine fossils, star-fish, mollusca, and various fishes, are of frequent occurrence. Animal and vegetable life during this period must have been very rich and varied—literally leaving “footprints in the sands of time.”

The “Blue Lias” is a term familiar to every reader. It is a kind of limestone mixed with clay, of a blue colour, and upon this we find the Oolitic, or Oolite System—so called because it somewhat resembles the roe of a fish. The Lias clays are used for bricks, and Whitby “jet” is also obtained from the Upper Lias. Jet is really a lignite, or wood in the process of transmutation. In this Lias formation, besides the numerous fossil remains already mentioned, we find the “snakestones” (ammonites), the stone-lily, and belemnites, with many nautili and shells.

The Oolite, or Jurassic, underlies the chalk, and overlies the Trias formation. The term “Jurassic” originates from the Jura range, which is almost entirely composed of Oolitic strata. These strata are greatly distorted by pressure, and when we reach Switzerland and the familiar Alps, we find gneiss, crystalline, limestones, and schists, into which the Oolite has been metamorphosed. The Oolite is divided into Upper, Middle, and Lower, consisting of the following:—

The Oolite formation (see Map) occupies a stretch of country in England extending from Yorkshire into Dorset. The Great Oolite holds the Fuller’s earth, and the Bath stone is also well known. The Stonesfield slate holds many remains of reptiles. It is a kind of shelly limestone, and is used for roofing purposes. The Forest Marble (so called from Wychwood Forest) is a sandy limestone holding marine fossils. It is used for ornaments. The Coral Rag and Oxford clay are rich in fossils, and the former, as its name implies, is composed of ancient coral reef. The Portland beds produce the well-known building stone. The Purbecks, of which there are three divisions, appear to have been deposited in fresh water, and occur in Dorsetshire.

All the Oolite strata supply organic remains. We have plants and ferns, reptiles, and a number of new genera of conchifera and cephalopods, star-fish, urchins, and the enormous bats, and the terrible megalosaurus, and the cetiosaurus, steneosaurus, and pliosaurus, of enormous size. One very remarkable bird has been found in the Bavarian limestone of this period; it is called the ArchÆopteryx, which is described as having a leg-bone and foot like the familiar birds, but the tail is lizard-like, with feathers springing from each joint. Sponges, corals, and fish, and many other forms of animal life are found in the Oolites. The reptiles must have had it all their own way in this period, for there were both carnivorous and vegetable feeders, and teeth of the pliosaurus have been found which measure fifteen inches, the jaws being six feet long. We have seen that corals must have built up their reefs in the waters, which then overlaid the land we call the United Kingdom.

There must have been great changes during this period, and the strata are chiefly marine. The Wealden formations are the exceptions, and in the fresh-water deposits insect forms abound. The appearance and variety of animal and vegetable life must have been curious and interesting.

The Weald or “Wold” of Kent is often spoken of, and it extends with the Surrey and Sussex Wealden formations for some distance. The strata are of fresh-water deposition, differing in this from the chalk, although the Wealden beds are included in the Cretaceous Group, which is composed as follows:—

The “Wealden” formation is divided into Hastings sand and Weald clay. The former consists of clay and sandy beds, and is observable at Hastings, and in the neighbourhood of Tunbridge. The Weald clay consists of blue and brown clays, with sandstone, and the limestone known as “Sussex Marble,” which is formed by the paludina of the rivers. There is another division often seen in Dorsetshire, and called the Punfield beds, which partake both of marine and fresh-water remains, which are distinct in the true Wealden and cretaceous formations, the former being of fresh, and the latter of salt-water origin.

The remains of enormous reptiles are numerous in the Wealden formations; crocodiles, lizards, turtles of gigantic size have been discovered, and most curious fossils have been disinterred in the Hastings district. The “Greensands” are separated by what is termed gault, a stiff blue clay found in Norfolk, Essex, and Kent. The Lower Greensand includes the well-known Kentish rag, or limestone, of which so many churches are built. The Upper Greensand is supposed to be a seashore deposit on the sides of an extensive ocean or sea, at the bottom of which the chalk was formed. After the Wealden beds were formed, they were covered by these greensand estuary-beds, or littoral strata. In these series new forms of life appeared, and the waters became the receptacle of myriads of mollusca, etc., which in time formed the great chalk cliffs and downs so often referred to. The chalk is interstratified with sand, which as “gault” and “greensand” was probably the sand of the ocean bed before the chalk was formed upon it, and the seas must have supported many marine reptiles, for stony “nodules,” or coprolites, which are the fossil excreta of the animals, are found, and now used for manure, after being buried for thousands of years. Examination of these remains has resulted in the discovery of the teeth and bones of fish which had been devoured by the gigantic reptiles. An illustration of a shell thus discovered is annexed.

We have in a former chapter spoken of the chalk and its formation. We know that it is composed of the minute foraminifera. The fossil remains are very numerous in chalk and all of a marine kind, such as the ammonites, belemnites, and such cephalopods, and the echinus, bivalve mollusca, crustacea, etc. We have occasionally flints appearing in the chalk, and this circumstance has given rise to some speculation as to how the flints got there, for they consist of nearly pure silica; and the theory of the petrifaction of sponges, madrepores, etc., has been started to account for their presence. Dr. Carpenter says: “It may be stated, as a fact beyond all question, that nodular flint and other analogous concretions (such as agates) may generally be considered as fossilised sponges or alcyonian zoophytes, since not only are their external forms and their superficial markings often highly characteristic of those organisms, but when sections of them are made sufficiently thin to be transparent, a spongy texture may be most distinctly recognised in their interior.”

It is now generally admitted that the decaying animal matter acts upon the silicious spiculÆ of sponges, etc., and the silica is thus deposited.

We may then surmise that at some very distant period the whole extent of the British Isles was submerged, as well as portions of the continent, and after the strata had been deposited the sea and land were disturbed by volcanic action. While the secondary strata were being deposited, very little relative alteration took place, as the deposits are seen to lie “conformably.” But when the great convulsion which upheaved the Apennines occurred, the chalk was raised as we find it in the cliffs and downs, which were the beds of seas. This is the last of the great convulsions which the earth has undergone, for the tertiary strata, which afterwards began to be deposited, rest in the hollows or basins (chiefly in the chalk) then left; the alterations in and since these deposits appear to consist chiefly of the upheaval of certain localities, the depression of others, the evaporation of inland lakes, and the wear and tear of the land from these causes, which are still in continuous action (as from the washing down of cliffs by the sea, and the formation of mud deposits at the mouths of rivers), or the volcanic agencies which in some places (as in Ireland) have cast up basalt over the chalk.

There is a sort of transition formation which is classed with the Cretaceous System, and termed “Maestricht,” after the town in Belgium. It appears that this is an upper chalk layer, an intermediary between the Secondary and Tertiary, and here on the banks of the Meuse we find the Mosasaurus, the “lizard of the Meuse,” of whose remains we give specimens in the illustration. This transition chalk—as we may call it to distinguish it—must have been laid down at a later period than the flinty chalk, and we find it in many places. It serves therefore as a fitting introduction to the Tertiary Period of Geological time.

The Tertiary Period.

We now enter upon a period when the animal creation attained its greatest development, the “Age of Mammals”; for they were then the kings of creation. The Tertiary Period is divided into three stages, viz.—

The Eocene, or the Dawning of the now existing creation.

The Miocene, or the Middle, or “minority” of existing creation.

The Pliocene, or the Recent, or still more developed period.

We will glance at them in that order, which Sir C. Lyell introduced.

The Eocene formation is shown in what is termed the “London Basin,” here illustrated by a section in which we find soft sands without fossils (Thanet Beds), and a kindred kind in Surrey, in which fossils (marine) are found. After these we get the “Reading and Woolwich” beds as we ascend. These are of clay and pebbles, etc., with river fossils. The Oldhaven beds are included on the map; they occur towards Blackheath and Herne Bay. The London clay is very stiff, and in some places blue. It is full of fossils of birds, beasts, fruits, and vegetables, trees, reptiles, and fish, and the variety of the organic remains appears to indicate the fact that at one time the Thames flowed through swampy ground to the sea, in which dwelt, in a warm climate, immense mammalia, such as the megatherium, glyptodon, tapir, etc., and some turtles of enormous size.

It is also on record from late observations that these immense animals were even mixed up, and almost fabulous creatures inhabited the land where England now is. We read of antelope-horses, lion-like bears, and camel-stags. The vegetation was then of a tropical kind, and in the deep forests and jungles these enormous animals—the mammoth dinotherium, and such species—roamed and plunged in the swamps at the mouth of the Thames. At length these types died away, and gave place to the elephant and the hippopotamus, and the climate by degrees became less warm, and still slowly decreased in temperature.

A glance at Sir C. Lyell’s “Principles of Geology” will show us how, as we examine the more modern strata, we find a great increase in the European lands, which may have been compensated by the submersion of the Pacific islands. During the period of the vegetation of the Secondary epochs, our climate (between the lias and the chalk) was favourable to a tropical growth. Enormous rivers flowed through our islands, and gigantic crocodiles, etc., with flying reptiles, were masters of the land. There were numerous fishes, but the reptiles did not appear in such very great numbers.

These large and elephantine animals must have existed while the climate of Northern Europe underwent some very considerable changes. We read of the woolly rhinoceros, and the hairy elephant, or mastodon, which has been found in Siberia. Reindeer appeared in England, and we know now that these animals inhabit cold countries. The mountains were considerably elevated during the latter Tertiary period; snow fell and ice formed upon the summits of the mountains, while glaciers crept down the sides. The warm, almost tropical climate of the prior ages was gradually but surely giving way to the Ice Age; the earth was slowly dipping, and the sun’s rays had less power.

Professor Ramsay says the “assemblage of fossils found in the London clay point to the fact that the whole of these strata were deposited in the estuary of a great continental river comparable to the Amazon and the Ganges. The palm-nuts and the host of other plants help to prove it, and the remains of river tortoises, crocodiles, snakes, marsupials, and several tapir-like mammals, all point in the same direction. The estuarine conditions begun during the deposit of the Woolwich and Reading beds were still going on when the London clay was thrown down; with this difference, that by sinking of the area the estuary had become longer, wider, and deeper, but still remained connected with a vast continent, through which the Eocene river flowed.”

The Miocene deposits are not so generally important in the United Kingdom, but in America very valuable fossils have been discovered in these strata. The Pliocene strata extend along the east of Great Britain, where they are denominated “Crag,” as Norfolk Crag, Red Crag, Coralline Crag. Underneath these mammalian remains have been discovered. After the Pliocene we come to the Post-Pliocene, which really closes the long Tertiary period. During these ages the gradual development of created beings apparently reached its height. It was towards the end of the Middle Eocene that the great mountain chain of Europe came into existence, which is connected, as any casual observer may see, with the Himalaya. In fact, the whole chain, from the Thibetian range through India, the Caucasus, Alps, and Pyrenees, is continuous, and formed of the same material (“nummulitic limestone”). There is no doubt that the whole northern hemisphere enjoyed at the commencement of the Tertiary period a warm, not to say tropical, climate, which got colder and colder.

We find the increase of animals and plants more fitted to the requirements of man and our present climate. There are many signs of the successive increase of land in Europe generally, while the contrast the Tertiary period bears to the Secondary is very marked. In the former we have extensive deposits in the waters of wide, open seas; in the latter the depositions were evidently made where dry land, with its accompanying bays and lakes, were extensive and numerous. The former is marine, the latter lacustrine and marine. The seas of the Tertiary period have lately been defined.

Sir Charles Lyell, in his “Principles of Geology,” shows us this, and defines the European features at the commencement of the Tertiary epoch. At that time, the British islands, with the exception of the basins of London, the Isle of Wight, and Norfolk, had wholly emerged from the deep. But a third part of France was still under water. Italy consisted only of a long and narrow ridgy peninsula, branching off from the Alps near Savona. Turkey and Greece, south of the Danube, were laid dry; and a tract of land extended from the Vosges, through central Germany, Bohemia, and the north of Hungary, perhaps to the Balkan. But the whole of the north of Europe and Asia, from Holland eastward to central Tartary, and from Saxony and the Carpathians northward to Sweden, Lapland, and the Ural chain, lay beneath the ocean. The same subterranean movements, which have subsequently raised the wide plains of our northern continents above the sea-level, have given great additional elevation to the then existing land. Thus the Alps have certainly acquired an increased height of from two thousand to four thousand feet since the commencement of the Tertiary period. The Pyrenees, whose highest ridge consists of marine calcareous beds, of the age of our chalk and greensand series, while the Tertiary strata at their foot are horizontal, and reach only the height of a few hundred feet above the sea, seem to have been entirely upheaved in the comparatively brief interval between the deposition of the chalk and these Tertiary strata. The Jura, also, owe a great part of their present elevation to convulsions which happened after the deposition of the Tertiary groups. On the other hand, it is possible that some mountain-chains may have been lowered by subsidence, as well as by meteoric degradation, during the same series of ages in this quarter of the globe; and on some points shallows may have been depressed into deep abysses. But, on the whole, everything tends to show that the great predominance of land which now distinguishes the northern hemisphere has been brought about only at a recent period, and Sir Charles holds that the shifting of the continents is sufficient to account for the variations of climate. We have every reason to believe that before the Glacial epoch England and the Continent were united, and during the Glacial period England and North America were joined, vi Greenland and Ireland. Mr. Dawkins says that England at that time was six hundred feet above its present level. If so—and we cannot question his conclusions—the Channel was then dry.

The “Great Ice Age” then came upon the world. For the information of readers who wish to peruse the whole history of this epoch and its causes, we may add that in Professor Geikie’s most interesting work, they will find full details. We can only refer to it.

The gradual decrease of temperature upon the earth, which was the cause of the Glacial period extending over the north of Europe, has been attributed to the eccentricity of the earth’s orbit; and here astronomy steps in to our assistance. We have read in the chapters on Astronomy, how the movement of the earth, like a top near the end of its “spin,” causes the “precession of the equinoxes,” and in connection with this phenomenon the earth’s orbit becomes more and more circular at certain periods of thousands of years, and goes away from the sun. We therefore receive the light and heat at a greater angle. Consequently, less heat is received, and ice is formed, as at the North and South Poles at present.

Doctor Croll has pointed out that the great eccentricity of the earth’s orbit existed about 210,000 years ago, when there was a difference between the nearest and farthest position of the earth and the sun of 12,000,000 of miles at least.28 This is a very considerable distance even in the enormous spaces which intervene between us and the other planets of the solar system, and about that time the Glacial period arrived. Perhaps we may make this clearer by going back to the precession of the equinoxes.

The earth moves in an orbit called an ellipse, and the sun is not in the centre of this nearly circular path. We can now understand that the earth comes nearer to the sun sometimes and recedes at others. These points of nearest approach and greatest distance are termed perihelion and aphelion. In the latter case we are about 9,000,000 of miles farther from the sun than when in perihelion—that is, when the greatest “eccentricity” is reached. In addition to this the axis of the earth is continually changing in direction by reason of solar attraction at the equator. This shifting, as explained in the astronomical section, is very slight every year, and in the course of 24,000 years the conditions of the seasons will have completely changed round and back again,—for the northern and southern conditions will be reversed in our hemisphere. Day and night come twenty minutes earlier every year. We are now nearer the sun in winter as shown in diagram (page 497); when we change we shall be nearest the sun in summer and farthest in winter.

Doctor Croll, who has done much in his most interesting paper on changes of climate29, tells us how this eccentricity of the earth’s orbit produced indirectly the Glacial epoch. He shows how, if in a period of the greatest “eccentricity” our winter came in aphelion, we should receive one-fifth less heat than now, but a correspondingly greater heat in summer. But if our winter under such circumstances fall (as now) in perihelion, the difference between winter and summer would be practically nil, because the sun during a period of the earth’s great eccentricity “could not warm the hemisphere whose summer happened to arrive in perihelion.” No doubt the sun’s rays would be very powerful, but the earth being covered with ice and snow could not be warmed; fogs would accrue and hide the sun, as at present in Antarctic summers, when the cold is very great. The warm ocean currents would be stopped, and the northern portion of our hemisphere would be, as it undoubtedly was, frozen over and covered with snow.

When we consider the millions of years since the earth is supposed to have been launched into space, we can imagine that the Glacial periods would occur frequently, and considering the very slow “precession” movement there, and the alternating tropical climate with graduations of temperature for thousands of years they would last long. The great Glacial period is computed to have begun 240,000 years ago and lasted 160,000 years with alternations of comparative summer; and so the years went on, season succeeding season, altering the appearance of the earth, and causing successive changes in the distribution of animal and vegetable life. Then the great mammalia, the mammoth and hippopotamus, with the hyÆna, lion, and other felidÆ came, and went when Arctic animals usurped their places. At the later Glacial epoch man must have arrived in Britain, and “this being so,” says Professor Geikie, “it is startling to recall in imagination those grand geological revolutions of which he must have been a witness.... He entered Britain at a time when our country was joined to Europe across the bed of the German Ocean; at a time when the winters were still severe enough to freeze over the rivers in the south of England; at a time when glaciers nestled in our upland and mountain valleys, and the Arctic mammalia occupied the land. He lived here long enough to witness a complete change of climate, to see the Arctic mammalia vanish from England, and the hippopotamus and its congeners take their places. At a later date, and while a mild and genial climate still continued, he beheld the sea slowly gain upon the land, until, little by little, step by step, a large portion of our country was submerged—a submergence which, as we know, reached in Wales to the extent of 1,300 feet or thereabouts.”

We find that the land underwent many subsequent changes; it rose from the sea, was again covered with ice, and many parts of Europe were devastated by immense glaciers—that of the Rhone extending for more than two hundred miles. Then came vegetation as the ice gave way, and luxuriance of the tropics reigned; more cold after that, then more heat, till the ice was finally driven to its mountain fastnesses, and “Britain for the last time became continental. Neolithic man came upon the scene; his palÆolithic predecessor had, as far as Britain and northern Europe are concerned, vanished for ever.” The inquiry respecting the arrival and presence of man in Britain would lead us too far in pursuit. The fact has been established that man was living in the Thames valley while tropical animals were in the country, and he has been classed by Professor Boyd-Dawkins amongst the mid-pleistocene mammalia, and at that distant period, man as man, and not as an intermediate form connecting the human race with the lower animals, was present in Europe.

The stone implements which have been found in river beds and in caverns, associated with the bones of various animals, such as the elephant, rhinoceros, hyÆna, bear, and others prove this. These very ancient and rudely-fashioned implements have been divided into two classes, the PalÆolithic and the Neolithic, by Sir John Lubbock. First the stone implements were used, and stone was superseded by bronze and iron. Then we come to the historic period. In the neolithic period we find stone implements in the lake dwellings of Switzerland and Constance (as well as the Lake of Neuchatel), all of which have lately developed many treasures. Bronze tools have also been found, and so the gradual progress of man as a fashioner of weapons can be traced from age to age.

From the “river-drift” man we descend to the cave-man, who is supposed to have been identical with the Esquimaux. When Britain became an island the cave-man seems to have disappeared from our country, and in the prehistoric age the earliest of the present inhabitants came here, and brought with them domestic animals; then the Celts of the bronze age, and then the iron. The wild beasts gradually disappeared, and domestic ones occupied their places under civilized conditions.30

So we come from the “Glacial period” to the open door of history through the antechamber of the prehistoric time.

The prehistoric is the arbitrary division between the post-pliocene or pleistocene and the known “historic” periods of the world’s history, and we must dismiss it with a few general remarks, for the changes which we have attempted to follow are still taking place in the earth; volcanoes and earthquakes are unsettling the strata, and adding to the physical and geographical record which will some day have to be written by posterity and future geologists. We can see in those prehistoric times traces of men (hunters and fishers) existing with difficulty, mayhap, in the midst of enormous quadrupeds, and fighting for existence with the bears and many other formidable foes. We have noticed the stone ages, the rough and the smooth as they may be called, and we can picture the primitive agriculture and work of the neolithic man. But it is by no means to be believed that neolithic man in Britain was a race all over the world. We may assume that in eastern climes the human race were in a more civilized condition as improvements made their way slowly westward. Our island history commences in the time of Julius CÆsar. Eastern chronicles go back many thousands of years farther.

It is so short a time, geologically speaking, since man appeared within the limits of history, that the earth’s changes, except from direct volcanic action or water erosion, are very trifling. The change is, as we said, continually proceeding; ceaselessly the earth is wearing away, and depositing her riches where she is undisturbed by civilization and man’s excavations and intrusions. The rock is worn by water; the grit is carried down and deposited to form sedimentary rocks as of old; the lime will continue to assist the coral to be built up; and the chalk cliffs will be born under the sea, and our organic remains shall be found to tell remote ages that we were an enlightened people. For all we can tell, and it is by no means unlikely another recurring cycle of Arctic and Tropical periods will in time pass over our earth; the bear and reindeer, the hippopotamus and the rhinoceros, may again inhabit our islands. If our generation be destroyed, the purely animal creation with the vegetable world will reign over the land, and new forests will deposit new coal measures for the support and comfort of a new generation of highly organized beings, when our remains shall have passed away to the borders of a “prehistoric” age.

We have seen in the foregoing brief sketch how the world has arrived at its present beautiful condition,—how it has been step by step prepared for us, how nature’s forces have been and are still working according to the immutable laws of the Universe. And, after all, how little we know! What scraps of intelligence only are we able to gather up from the boundless quantity of material which must have been laid down, yet what wondrous results scientists have been able to adduce from even these comparatively scanty specimens! The sea and land are ever telling us the same old story. Man’s research and Bible teaching are found hand in hand in cordial and reverent agreement. Nothing is altered since the day that the Divine command, “Let there be light,” went forth into space, and till the earth be destroyed the same forces will continue in operation, guided by the Hand that made it—“ever faithful, ever sure.”