The sabre-toothed tiger, the sharp tusks of which, six to eight inches long, made it a far more ferocious beast than any modern tiger of tropical jungles, was a Quaternary inhabitant of Europe and America. So was a smaller tiger, and a lion. The Irish elk, which stood eleven feet high, with antlers that spread ten feet apart at the tips, was monarch in the deer family, which had several different species on both continents. Wild horses and wild cattle, one or two of great size, roamed the woods, while rhinos and the hippopotamus kept near the water-courses. Hyenas skulked in the shadows, and acted as scavengers where the great beasts of prey had feasted. Sloths and cuirassed animals, like giant armadillos, lived in America. Among bears was one, the cave bear, larger than the grizzly. True monkeys climbed the trees. Flamingo, parrots, and tall secretary birds followed the giant _gastornis_, the ancestor of wading birds and ostriches, which stood ten feet high, but had wings as small and useless as the auk of later times. With the entrance of the modern types of trees, came other flowering plants, and with them the insects that live on the nectar of flowers. Through a long line of primitive forms, now extinct, flowering plants and their insect friends conform to modern types. The record is written in the great stone book. The Age of Mammals in America and Europe ended with the gradual rise of the continental areas, and a fall of temperature that ushered in the Ice Age. With the death of tropical vegetation, the giant mammals passed away. THE HORSE AND HIS ANCESTORS Every city has a horse market, where you may look over hundreds of animals and select one of any colour, size, or kind. The least in size and weight is the Shetland pony, which one man buys for his children to drive or ride. Another man wants a long-legged, deep-chested hunter. Another wants heavy draught-horses, with legs like great pillars under them, and thick, muscular necks--horses weighing nearly a ton apiece and able to draw the heaviest trucks. What a contrast between these slow but powerful animals and the graceful, prancing racer with legs like pipe-stems--fleet and agile, but not strong enough to draw a heavy load! All these different breeds of horses have been developed since man succeeded in capturing the wild horse and making it help him. Man himself was still a savage, and he had to fight with wild beasts, as if he were one of them, until he discovered that he could conquer them by some power higher than physical strength. From this point on, human intelligence has been the power that rules the lower animals. Its gradual development is the story of the advance of civilization on the earth. Through unknown thousands of years it has gone on, and it is not yet finished. [Illustration: _By permission of the American Museum of Natural History_