1 _Ammonite._ 2 3 4 _Foraminifera_ (_Chalk-builders_).] Now we take one more step upwards into almost a new world—the world on which mighty animals lived, and which man came to share with them. THE TERTIARY PERIOD. The reign of the reptiles is now passed. The ichthyosaurus and pterodactyl no longer inhabited the seas and continents. Great changes had taken place in the shape of the land. A river larger than the Rhine swept majestically through England from the borders of Wales right out into the German Ocean, and its banks were covered with forests and marshes, where the new animals which had come to take possession of the earth lived and moved and had their being. The mountains of the Pyrenees were raised above the sea, and parts of Surrey and Sussex appeared too. It was most likely in the early part of the Tertiary period that the stone was formed of which almost all Paris is built. Fancy a great city built of the shells of dead animals! One can scarcely believe it: but the microscope lets us into this secret of Nature. If we take a piece of this stone and examine it in a powerful microscope we see that it is made almost entirely of tiny shells, so small that myriads of them could be packed in a nut-shell. How long must they have been working to make all the stone beds of which Paris is built? We cannot measure the time, we can only know it must have been enormous! All kinds of animals both of sea and land increased in numbers and perfection. The ammonites were dead, but their even more beautiful relation, the nautilus, was living as it is now. The trilobite was gone, but his next relation, the lobster and crab, appeared. Fishes abounded. Whales which suckle their young ones appeared, and the numbers of vertebrata, or animals with backbones, were more numerous than they had ever been before. Just as animals with bones are more perfect than those with only skins or shells, so animals which suckle their young ones are more perfect than those which only lay eggs. Thus the whale is a more perfect animal than the shark, though both inhabit the water; and elephants and even rats and mice more perfect still; and because there were so many of these “sucklers,” or mammalia as they are called, in the Tertiary period, we know that all living creatures were becoming more perfect. It will interest you too to learn that monkeys began to appear now, and that they were common in France, while at the present time the only part of Europe where they are to be found is on the rock of Gibraltar. But I want particularly to tell you of the giant animals—the Mammoth, Mastodon, Megatherium, Dinotherium, and others, and first let us see what the mammoth was like.