CHANGES OF LAND AND WATER 



The reason why the ancestral forms died 

 out is really connected with the general change 

 in the surface of the earth. New forms have 

 gradually taken the place of the old forms — for 

 no piece of land remains the same for many 

 years. A thousand years, as I have said, in 

 this matter is merely nothing, but even in a 

 thousand years we get great changes in the 

 surface of the land. Land may rise far above 

 the sea, and what was an island become part of 

 a continent. And what was part of a continent 

 may partly sink, and become an island — that is, 

 the connexion between it and the continent may 

 become covered with water ; and then the 

 conditions of life for the animals are very much 

 changed. Such currents as the Gulf Stream 

 are affected by this alteration in land and 

 water. Were certain changes to take place, 

 the Avarm w^ater of the Gulf Stream would no 

 longer warm certain land ; the climate would 

 become colder than the animals have been 

 accustomed to. The animals that could not 

 stand the cold would die out, whilst those that 

 could stand the cold would flourish.^ All I 



^ A fish — the Tile-fish — living in the Atlantic, near the 

 North American coast, was destroyed in this way a few 



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