It was not a display of life to excite our imaginations. There was nothing that ran or flew or even swam swiftly or skilfully. Except for the size of some of the creatures, it was not very different from, and rather less various than, the kind of life a student would gather from any summer-time ditch nowadays for microscopic examination. Such was the life of the shallow seas through a hundred million years or more in the early Palæozoic period. The land during that time was apparently absolutely barren. We find no trace nor hint of land life. Everything that lived in those days lived under water for most or all of its life. [Illustration: Life in the Early Palæozoic Note its general resemblance, except for size, to the microscopic summer ditch-water life of to-day.] Between the formation of these Lower Palæozoic rocks in which the sea scorpion and trilobite ruled, and our own time, there have intervened almost immeasurable ages, represented by layers and masses of sedimentary rocks. There are first the Upper Palæozoic Rocks, and above these the geologists distinguish two great divisions. Next above the Palæozoic come the Mesozoic (middle life) rocks, a second vast system of fossil-bearing rocks, representing perhaps a hundred millions of swift years, and containing a wonderful array of fossil remains, bones of giant reptiles and the like, which we will presently describe; and above these again are the Cainozoic (recent life) rocks, a third great volume in the history of life, an unfinished volume of which the sand and mud that was carried out to sea yesterday by the rivers of the world, to bury the bones and scales and bodies and tracks that will become at last fossils of the things of to-day, constitute the last written leaf. (It is, we may note, the practice of many geologists to make a break between the rest of the Cainozoic system of rocks and those which contain traces of humanity, which latter are cut off as a separate system under the name of Quaternary. But that, as we shall see, is rather like taking the last page of a book, which is really the conclusion of the last chapter, and making a separate chapter of it and calling it the last chapter.)