Palms and species like the big tree of California were growing side by side with species akin to our own common trees. But in the animal world there were many strange forms. This was the age of reptiles. They domineered on the land, in the air, and in the sea. On the land there stalked huge reptiles fifty and sixty feet long, and, when standing erect, at least thirty feet high.15 Some of these huge creatures were carnivorous, living on other animals. Others fed on the foliage of trees. In the air, huge reptilian bats, veritable flying dragons with a spread of wings from ten to twenty feet, disported themselves.16 In the sea there swam great reptilian whales, seals, and walruses.17 There was a marvelous abundance of reptilian life. At the present day, there are not more than six species of reptiles in the whole world having a length of over fifteen feet, and not more than eighteen species exceeding ten feet in length. But from one limited locality, representing but one era of this age in England, there have been discovered four or five species of carnivorous reptiles twenty to fifty feet long, ten or twelve species of crocodiles, lizards, and swimming reptiles from ten to sixty feet long—besides multitudes of great flying reptiles and turtles. Doubtless similar scenes of animal life were everywhere represented. The Labyrinthodon. Birds made their first appearance during the Mesozoic time, and here we obtain a clear view of nature’s methods of work. There is no longer a doubt but that the first birds were simply modified reptiles. The first bird had a long jointed tail, and a bill well supplied with formidable teeth.18 It was during this period that the first representative of the class Mammalia, to which man belongs, appears.19 It is in the rocks of this era that we meet with remains of marsupials, the order to which opossums belong. This is the lowest of the Mammalian class. To the class Mammalia belong the most highly organized animals. They have been the ruling animals since the close of Mesozoic time. We must now watch their development with especial care. For this brief review, as far as it has gone, has shown a steady and gradual progress in life forms, the lower invariably preceding the higher. We therefore feel that it will be vain to seek for any trace of man until we find undoubted proofs of the existence of all the forms of animals below him. The last great division of time is called Cenozoic.20 This means new life forms. In this age, the forms of life are much nearer our own. As it was some time during this epoch when man makes his appearance, we deem it best to go into more detail, and give the subdivisions of this period.