Page:History of Iowa From the Earliest Times to the Beginning of the Twentieth Century Volume 1.djvu/39



found. The sediment exposed to the action of the atmosphere has been converted into vast plains and prairies. In many cases the lakes have been gradually filled and converted into dry land. Modern streams, such as the Yellowstone, Missouri and the Platte rivers cut their way through these old lake beds. The surface of the sediment underwent continual changes through erosion. The remains of plants and animals were thus slowly laid bare, and the scientist was able to read the story of their lives. Such beds are believed to be the only places of importance where the records of Tertiary plants and animals have been preserved. While none of these lake beds have been found within the limits of our State, it cannot be doubted that the conditions which prevailed upon our western and northern boundaries were not unlike those which obtained here.

The animal inhabitants of this period consisted of opossums, a strange species of squirrel, beavers and gophers. There were large hoofed animals not unlike the rhinoceros; others bore resemblance to the tapir and the swine family. There were creatures with three hoofs to each foot and three toes on each hoof, of a species related to the horse. There were others resembling camels, oxen and cud-chewing animals that seemed to be a combination of the deer, the camel and the hog. There was a family of short jawed animals resembling the panther with sharp, knife-like teeth. There were saber-toothed tigers more powerful and cruel than the Asiatic species; there were monkeys, foxes and wolves. Huge snakes, lizards and turtles infested the swamps. Bright winged birds flitted among the forests and open glades. Bats and myriads of strange insects were present preying upon others.

Throughout the Tertiary period the climatic conditions appear to have been remarkably uniform over regions extending north to Greenland and westward to Montana. Iowa, and all adjacent regions far north and westward reveled in the luxuriance of a tropical climate. The air