Curious ideas about fossils—The pages of the Earth's history—Interesting finds within the Earth—The ancestors of the horse—The ancestors of the birds—Gigantic reptiles rule the Earth—Life when the coal-fields were being laid down—Abundance of fish—Curious extinct fish—Poverty of life in lowest deposits—The origin of life

In the preceding chapter we have seen that the discovery of fossils is not of recent date. The ancients found fossil shells and fossil fish, and some of the earlier philosophers really discovered the meaning of these. So long ago as two thousand five hundred years the presence of these buried fossils was declared to be a proof that those portions of the Earth had formed the bed of an ocean at some earlier date. At the same time many ancient writers had very fantastic ideas concerning the Earth. However, there were books written upon the subject of fossils before the dawn of the Christian Era.

Nearly two thousand years after the declarations of the early philosophers (to be more exact, in the fifteenth century) there arose great disputes concerning fossils. Some scientists argued that fossils were merely freaks of nature, while others even suggested that they were carved stones, Other philosophers, whom we know to have been in the right, declared that the marine organisms that had lived in the shells had inhabited the ocean exactly where the shells were buried. These disputes were not settled easily, and long after geologists were convinced of the origin of fossils, the facts were disputed from the religious side, these wranglings being still in evidence in the days of our grandfathers.

The different layers of geological deposit may be regarded as the different pages of the Earth's history. The deposits nearer the surface are naturally the later pages, while the deeper layers give us the earlier history.

Our present object is to consider what has been discovered concerning the early life upon this planet. It is fortunate that it is not necessary to dig down into the different deposits in order to read this history. If this had been necessary we should never have been able to open anything but the later pages; the lower deposits would have remained a sealed book. The book has opened of itself at a great many places, for as mentioned in the preceding chapter, the lower strata have been forced to the surface and project through the outer crust. It does not matter if the layers are no longer in a horizontal position; their relative position is perfectly clear, and that is all we require.

Turning the pages of this great history backwards, we are not surprised to find that the fossil remains which have been discovered in the uppermost deposits are well represented by living animals with which we are familiar. We find among these the fossil remain l of lions, bears, wolves, horses, dogs, deer, reindeer, bisons, camels, hares, weasels, mice, and such-like. From the discovery of these we learn that all these contemporaries of ours lived also in ages long past.

We find also the fossil remains of existing birds, such as the eagle, goose, duck, pigeon, ostrich, and so on. But in addition to all these we find the remains of some gigantic animals similar to the elephant, but now quite extinct. Traces of these "mammoths" or woolly elephants are found sometimes not very far from the present surface of the Earth. Men, busy digging the foundations of buildings in some of our large cities, have discovered the fossil remains of extinct animals. In Australia the uppermost layers show that kangaroos were at one time twice as large as at present.

It will be understood that even some of these later pages of the Earth's history take us back a few million years. We have seen that among these deposits we find horses very similar to our domesticated friends of to-day, but as we go to deeper layers we find horses with three toes on each foot, only the centre toe being capable of touching the ground. Still lower we find that their ancestors had as many as four toes, all capable of resting on the ground, but these horse-like animals are no bigger than a child's rocking-horse of small size. Lower still we find the fossil remains of a more primitive horse, no bigger than those toy horses which very little children delight to pull along the nursery floor. But we must not picture a miniature horse such as the toy. This small ancestor of the horse, measuring about one foot in height, was considerably different in appearance from the horse as we know it to-day. His head and neck were shorter, and his back was curved upwards, yet his fossil remains show quite clearly that he was a direct ancestor of the horse of to-day. The words "direct ancestor" are used here in a different sense than in such terms as "our great-great-great-grandfather"; this ancestor of the horse lived some millions of years ago, long before man inhabited the Earth. By means of other fossil remains we can trace the ancestry of the elephant, the pig, the rat, and many other classes of animals.

Among the fossils of these uppermost deposits, we find a great abundance of fish, serpents, crocodiles, and tortoises. In addition to the ordinary birds, already mentioned, we find some extinct birds with traces of teeth, and still lower down we find birds with teeth. In this turning back of the Earth's history book we have already reached a time some millions of years ago.

If we continue the downward search for birds, we find some strange-looking specimens, not only armed with teeth, but having three claws at the corner of each wing, and although they have feathered coats they possess long lizard-like tails. These strange birds are not large, being about the size of an ordinary pigeon. Some of the birds had no wings, and evidently swam about on the waters all their lives. Continuing this search backwards, and keeping a look-out for fossils of birds, we find that earlier than this period there were no real birds. There are complete skeletons of what can only be described as flying lizards. These have no feathers, and their bat-like wings, when spread for flight, must have measured in some cases as much as twenty feet from tip to tip. Some of these flying reptiles grew to an enormous size; some authorities estimate them at sixty feet from the point of the nose to the end of the tail. The sitting-room in an average dwelling-house is only about twenty feet, so that one may gather a fair idea of the size of these flying reptiles. When we remember that reptiles keep on growing as long as they live, we have only to presume a very long life for these creatures to enable them to reach such proportions. In the deposits of an earlier date we find no sign of birds, and it is clear that their earlier ancestors were true reptiles. By this time we have reached a very remote period.

Before that time we have lost trace of any forms of apes, which had become more and more primitive as we descended. We find only traces of mammals, or breast-animals. We still find reptiles which, of course, are egg-laying animals, and do not suckle their young as the mammalians do. The reptiles in these lower deposits are the largest ever known. Some excellent skeletons of these have been discovered, and with the knowledge obtained from these Dr. Carl Hagenbeck, of Hamburg, has made life-size models representing the actual creatures.

In the illustration facing page 58 we see one of these models under construction, and this picture gives us a good estimate of the size of the great creature. In the illustration facing this page we see the complete model as it stands in the Hamburg Tierpark. This "Diplodocus," which measures eighty feet in length, is not the largest animal of that period. It was a very harmless vegetarian, whereas there were gigantic land animals, such as the "Allosaurus," seen in the illustration facing page 62. Some of these land animals had powers of destruction which must have put terror into the lives of the smaller creatures living within their reach. Of course, there are living animals of to-day with huge bodies, such as the elephant, the hippopotamus, and the whale.

It seems probable that during the period when reptiles ruled the Earth the land became so crowded that some land animals had to take to the sea as a dwelling, while others took to the air, very gradually evolving wings, until their descendants became more birds than reptiles.

Still farther back we find reptiles of a much clumsier make, and it is apparent that some of them had paddles to propel them through the water. These were preceded by similar reptiles, but having feet in place of paddles, the feet being evolved into paddles when the animals left the land for the surface of the sea.

Still farther back we find abundance of amphibious creatures, capable of living under the water or on dry land as they desired. We may think of them as frog-like animals. During this period there was a comparative scarcity of animal life.

Below this we come upon the great coal-beds of the world. From what has been said, at the close of the preceding chapter, of the heated moist atmosphere, we are not surprised to learn that there were plenty of snake-like creatures which could live in the swamps of the gigantic forests. There were present also a great variety of shark-like creatures and lung-fish. There are fossils of land snails which probably made their homes on the trees, while there is evidence of spiders, beetles, and other insects that could live in a watery atmosphere. The gigantic vegetation was of a simple form, with large leaves measuring about twenty inches across. But even with this enormous growth of vegetable life the great accumulations required to form the coal-beds must have taken many thousands of years to produce.

Lower down than the coal-beds we find fish more abundant than ever. Some of these are as long as eighteen feet and are provided with jaws of enamelled bone, which evidently could be used like shear-blades. Fish are said by some never to reach an adult size, but, like the reptiles, they grow till death. The humorist might add that in our own days the fish caught by some enthusiastic anglers continue to grow even after death.

Along with these early fish we find gigantic crabs, some measuring six feet across, and as we go farther back we find fish protected on the head and shoulders with plates of bone. Still lower down we discover fish completely armoured in this fashion, and it is interesting to know that our contemporaries, the sea-urchins, had direct ancestors living away back in those far-off times. We have proof that there was some land vegetation at that time, as there are fossil remains of insects.

In our backward search we come across even more primitive types of plated fish, and an abundance of a very simple form of crab-like creatures, which we call "Trilobites." These were strange-looking creatures, some measuring about two feet in length, and having their bodies divided into three lobes. They had eyes, and could move or roll about. A few descendants of these are found as high up as the coal-bed period, but it is in the lower deposits that they are plentiful, even when there are no traces of fish at all, not even the simple forms of boneless fish, unless that class which we describe as star-fish.

In these lower deposits we find no trace of land animals, not even insects, and from this we gather that what land there was above water was probably too barren to support animal life. In the lowest deposits we find no traces of life. But the first forms of life would be of soft, jelly-like material, and would leave no record.

In the address of Professor Schafer at the Dundee meeting of the British Association in 1912, he dealt exhaustively with the subject of the origin of life upon this planet. His belief is that life was evolved very gradually from lifeless matter, and that its first appearance would be as a mass of colloidal slime, which could assimilate other matter and therefore grow, and by subdividing it could reproduce itself. But these philosophical conceptions of the origin of life are without the scope of actual discovery.