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.