14 THE OCEAN FLOOR 



and has a maximum saddle depth of less than 200 feet. 

 During the great glaciations of Quaternary time, when 

 enormous masses of water were transferred from the 

 oceans to the inland ice, the ocean surface is generally 

 admitted to have sunk about 250 feet, some authorities 

 claiming a still greater lowering. This would imply that 

 unless there was a corresponding sinking of the bottom 



Fig. 6. Distribution of ocean and land in Mesozoikum 



of Behring Strait one might have walked across dryshod 

 a few hundred thousand years ago. It is generally as- 

 sumed that an invasion from Asia into North America, 

 both of animals and of men, took place over this sub- 

 arctic land bridge, so that the ancestors of the Indian 

 population of the New World may have crossed thus 

 from one continent to the other. 



As for the Indian Ocean, very radical attempts at a 



