Thus we see what a great advance was made in life during this period. The forms of life during the early stages of this age were inferior in this, also, that they were all water species.11 But, before it closes, we have a rich and varied terrestrial vegetation, and also air-breathing animals. The class Mammalia, to which man belongs, had no representative on the earth during the extended Paleozoic time.
We can easily see, from the foregoing, how appropriately this period has been named that of old life forms. In imagination we can recall a scene of this old age. The air is sultry and full of vapors. The soil seems hot and steaming. This is a veritable forest, but we see none of the beautiful flowers which we associate with tropical vegetation to-day. In the branches of the graceful tree-ferns, we will look in vain for birds. They were yet far in the future. Neither were there any of the higher orders of animals present. Not a single representative of the great class of mammals enlivened the depths of the forest. There were fishes in the waters, but not the fishes of to-day. Some true reptiles and amphibians disported themselves in swampy jungles, but they were unimportant. Almost the only sound to break the stillness, was the hum of marsh-loving insects, the whistling of the wind, and the roar of the tempests, which we may well believe raged with the more than tropic severity of the present.12
The time at last came for the dawning of a new era. Vast changes had been taking place in the geography of both continents. The region to the south-west of the Green Mountains was upturned. The Alleghany Mountains were formed, and the region east of the Mississippi River became part of the stable land of the continent.13 In Europe, nearly as great changes occurred. The conditions of life must have been greatly modified by these geographical changes. The life-forms bear testimony to this changed condition. Old forms die away, and are succeeded by those approaching more nearly our own times. The name of this period is the Mesozoic time, or the period of middle life forms.14 It is instructive to notice the steady advance in the type of life, both animal and vegetable. The abundant flowerless vegetation of the coal formation of the preceding epoch dwindles away. But the flowering trees increase in number and importance until, in the closing period of Mesozoic time, we have trees with deciduous leaves. A great many of our forest trees had representatives in the forests of that epoch.