HUNTING FOR ANIMALS OF PAST AGES 33 



species of mammal immigrants. My boy," he 

 said, turning to me, "if you will keep on explor- 

 ing you will find hundreds of other exciting facts 

 in fossils, both afield and in books." 



One day the cook, in fishing about a quarter of 

 a mile below camp, discovered a fossil which 

 turned out to be a part of Miohippus, the little 

 Oligocene horse. In joking him concerning 

 his horse he offered to give it to me if I would 

 find a Chalicothere. He suddenly asked, "What 

 would you feed a Chalicothere? Giraffe, horse, 

 or bear feed, or would you mix these and make 

 him a prehistoric hash?" 



I often puzzled over how it was possible to 

 tell the age in which any fossil animal had lived. 

 There were perhaps one hundred past ages of 

 prehistoric life. Fossils of animals from fifty 

 thousand years ago had been found, and fossils 

 perhaps millions and more likely a billion or more 

 years old had been discovered. 



One evening a number of us planned to get 

 the scientist to talk at the camp-fire about fos- 

 sils and the different ages, chiefly for the benefit 

 of the cook and myself. 



"Fossils," he said, "are known somewhat 

 after the manner of clothes. Each year or pe- 

 riod has its particular cut. Most fossils are 

 found in sedimentary rocks limestones, sand- 

 stones, conglomerates, and schists. During the 



