The Romance of Modern Geology / Describing in simple but exact language the making of the earth with some account of prehistoric animal life

by Edwin Sharpe Grew

The heavy armour of the head of the Triceratops must have been developed for purposes of attack and defence, but we do not know whether it was for fighting their own species or for protection against the carnivorous reptiles. "So long," says Professor F. A. Lucas, "as Triceratops faced an adversary he must have been practically invulnerable, but, as he was the largest animal of his time, it is probable that his combats were mainly with those of his own kind, and the subject of dispute some fair female upon whom rival suitors had cast covetous eyes. What a sight it would have been to have seen two of these big brutes in mortal combat, as they charged upon each other with all the impetus to be derived from ten tons of infuriate flesh! We may picture to ourselves horn clashing upon horn, or glancing from each bony shield until some skilful stroke or unlucky slip placed one combatant at the mercy of his adversary....

"A pair of Triceratops's horns in the National Museum (at Washington) bears witness to such encounters, for one is broken midway between tip and base; and that it was broken during life is evident from the fact that the stump is healed and rounded over, while the size of the horns shows that their owner reached a ripe old age."

In connection with the concluding part of the last sentence it should be mentioned that reptiles, like fishes, but unlike birds and mammals, continue to grow throughout their entire span of life, so that unusually large bodily size is, at all events as a rule, an indication of advanced age. As regards general appearance Triceratops may, perhaps, be best described as a reptilian rhinoceros, with the proviso that the tail was much larger and thicker than in that group of animals, and passed insensibly into the body, as in reptiles generally, while the number and arrangement of the horns were different.

The Pterosaurs, or flying reptiles, made, as we have said elsewhere, a great advance. Williston regards them as having come to excel all other flying vertebrate animals. Some attained a wing-spread of twenty feet, and they could fly far and fast. They were all short-tailed; some of them probably could scarcely walk, and the larger of them had no teeth. Their bills resembled those of modern birds, and they have been styled the kingfishers of the Cretaceous seas. Terrific to look upon, they were probably not very deadly animals except to small fishes. The lizards did not make much progress; but the snakes made their first appearance, though they remained small; and the mammals showed little progress from the forms which were found in the previous era of the Jurassic.

At the close of the geological period whose natural physiognomy we have thus traced, Europe was still far from displaying the configuration which it now presents. A map of the period would represent the great basin of Paris (with the exception of a zone of Chalk), the whole of Switzerland, the greater part of Spain and Italy, the whole of Belgium, Holland, Prussia, Hungary, Wallachia, and Northern Russia as one vast sheet of water. A band of Jurassic rocks still connected France and England at Cherbourg—which disappeared at a later period, and caused the separation of the British Islands from what is now France.

CHAPTER XXII

THE AGE OF MAMMALS

The Geological Record is not perfect. There are breaks in it such as have not and may never be filled up; and it is because of these breaks that some of the divisions are made in geologic time. At present the earth's crust has only been scratched for fossils. Great parts of Asia and of Africa and of South America remain to be explored, and they may in some future generation fill the gaps of our knowledge and render superfluous some of the divisions which geologists now place in the eras of the rocks and of the fossils. But so far as we know at present there were real breaks in the history of the continents, perhaps not swift or sudden, but wholly changing the appearance and the life, vegetable and animal, of half a world, perhaps the whole world at a time. Many geologists believe that the secret of these changes lies in the core of the earth; and that, to use our old simile of the golf ball, when the tension and pressures inside the earth grow too much for its strength something gives way, and the whole world begins to change, the continents sinking under the oceans and new lands arising. We shall not again consider this idea in all its bearings, or ask whether there is any simpler explanation to be found in the never-ceasing explosive tremors of the crust; but we shall only say that the last of these great changes set in at the end of the Chalk age. After that era we arrive at the period among the rocks which, with all its subdivisions, Eocene, Miocene, Pliocene, Quaternary, is classed as Cainozoic or Modern.

Let us sum up the changes broadly. The Tertiary period, which now begins, has been called the Age of Lakes: but this merely means that there were great lake deposits, and it is true to say that as contrasted with a period of great waters, the Tertiary is to be considered as the period of land. That does not mean that there were in all the hundreds of thousands of years which it embraces no advances and retreats of the sea, no submergings and uprisings of the land. There certainly were. But the land was dominant, and it is the land animals and the land vegetation that are the most important and progress most. After the earth movements which occurred at the end of the Mesozoic or Secondary period there appears to have followed a period of quiet. There was a considerable area of land standing high above the waters; and there began one of the minor but considerable encroachments of the sea in North America. It is probable that the Pacific and the Atlantic joined between North and South America. At the end of this first period the sea withdrew again, and what is called the Miocene period began with a lowering of the temperature of the waters of the Atlantic; and lastly followed the great extension of the land towards the north, the great withdrawal of the sea of Pliocene times, and the growing cold which led to the glacial era of the Pleistocene period. In Europe and in Asia we may note that the great areas which are now covered by the Alps and the Himalayas were at the beginning of the Tertiary period still under water and only a few signs (in the form of islands) of these mighty ranges were beginning to appear.

Pre-eminently the age which comprises all these periods is the Age of Mammals. But one of the changes which European geologists first noticed was the surprising change which took place in the marine fossils. The animals of the sea which were familiar during the Chalk period nearly all disappeared and were replaced by new ones. The great saurian reptiles, from the monsters of the land to the mososaurus serpents of the sea, disappeared, and most other reptiles showed profound changes, showing a revolution in the animals of the land corresponding to that of the sea. Lastly, in this first period, the Eocene, mammals suddenly appear in force and occupy the first place among the animals. The vegetation did not change so much as might have been expected.