The Story of the Rocks 



149 



formed the route of migration of many forms between the 

 old world and the new. Why the camels should have left 

 their birthplace in North America and wandered forth to the 

 ends of the earth is a mystery, as are so many other prob- 

 lems in the history of animals as well as in that of man. So 

 too the horse, whose earliest home is uncertain, underwent 

 his great evolutionary development in North America, whence 

 he migrated from time to time into South America, Europe, 

 Asia, and Africa, and finally disappeared from his ancestral 

 home, only to be re-established there by the agency of man. 



EARLY DAYS IN THE TAR POOLS OF SOUTHERN CALIFORNIA 

 A saber toothed tiger and giant wolf contesting the carcass of an 

 elephant while condors are waiting nearby, until victor and vanquished 

 alike shall have fallen victims to the tar. From an illustration by 

 Horsfall in Scott's ''History of Land Mammals in the Western Hemi- 

 sphere. ' ' 



By permission of the Hacmillan Company. 



Here we encounter another unsolved problem in palaeontol- 

 ogy the extinction of the horse in the Americas. Glacial 

 conditions alone would seem inadequate, nor does there seem 

 to have been a sufficient development of larger carnivores to 

 explain it. So some sort of a pestilence has been called in 

 to aid in the explanation, but this is merely a recourse to the 

 unknown, a last stand of the defeated philosopher, when no 

 available facts will serve his purpose. 



Thus in the "sands of time" as well as in flesh and bone 



