174 EVOLUTION OF TO-DAY. 



short time before the present geological epoch the 

 northern continents possessed a fauna very different 

 from that now found there. Over Europe lived a 

 fauna closely resembling that now found in Africa 

 and India, and North America similarly contained 

 animals now belonging to South America. At this 

 time the northern and southern continents differed 

 very little from each other. Elephants, giraffes, 

 hippopotamuses lived all through Europe; tapirs, 

 great tigers, llamas, edentates, existed in great 

 numbers in North America. Since that time there 

 has been a remarkable change, and one which 

 appears to have been quite sudden. But it is a change 

 which has received a happy explanation, for this 

 wide distribution of tropical animals occurred just 

 before the glacial period. Geologists have agreed 

 that not long before the present era the northern 

 parts of the northern continents were covered with 

 great sheets of ice which gradually travelled south- 

 ward, covering much of Europe and North America, 

 and producing great physical changes of every kind. 

 This southward moving glacial mass is seen at once 

 to be a perfect explanation of many of the differen- 

 ces between the present fauna of the northern con- 

 tinents and that of older times. With the advance 

 of the ice and the consequent fall in temperature, all 

 animals and plants must have been driven farther 

 and farther south. Many were destroyed alto- 

 gether, not being able to find a suitable climate. 

 Some were driven into South America and Africa, 

 and, finding here favorable conditions, they continued 

 to live and multiply. When at last the ice once more 



