142 MIGHTY ANIMALS 



the same direction to escape the extreme cold. It 

 was after the ice had drifted north again that the 

 sloths and other South American animals came 

 into North America. Then once more the ice began 

 to drift south, and many animals again journeyed 

 into South America, where the climate was warmer. 

 It took many thousands of years for all these 

 changes in climate to occur, and when animals 

 shifted their homes from South America to North 

 America, they may have lived north for many 

 hundreds of years before they felt the effects of 

 the slowly approaching ice. After the last retreat 

 of the ice northward, the Mastodon still lived on in 

 the northeastern part of the United States. And 

 about this time the horse, which, for thousands of 

 years had been developing in this country, mi- 

 grated to some other country, although just where 

 he went we do not know. Nor were there ever any 

 other horses in America until they were brought 

 here by the Spaniards. 



As the centuries rolled by, all the gigantic animals 

 we have been learning about completely disappeared 

 from the face of the earth, and man, at last, became 



