OLD ROADS TO A NEW ISLAND 13 



time they could not cross from one land to another, 

 and in those years when they could not mix 

 together they grew to be less and less alike. In 

 North America the old camel family died out, 

 while in South America the same family grew 

 into the llama and the guanaco. In South 

 America the rodent family flourished in many 

 sizes and shapes. In North America we think 

 of a rat as a large rodent, but on the other side 

 of Panama some rodents grew four and five feet 

 long. There came to be very few kinds of deer 

 in South America. The catfishes are much more 

 important among the water animals than they 

 are farther north. Running birds, somewhat like 

 ostriches, live wild in South America, and opossum- 

 like animals, that carry their young in pouches, 

 are more common there than with us. 



It seems quite certain from the story of the 

 rocks that the Isthmus of Panama was under 

 water the last time many thousands of years ago. 

 If Columbus had lived so long ago he might have 

 found his waterway to India then; but, so far as 

 we know, there were at that time no men on the 

 earth yet. The land has not stayed at the same 

 height since the last ocean connection was broken. 

 Sometimes it rises, sometimes it sinks, and again 

 it stands quiet long enough for the ocean to build 

 up great beaches. Judging from these old beaches, 

 the land has been slowly rising for the last 

 thousand vears at the rate of three feet in a 



