376 THE BOTTOM OF THE SEA. 



will reach Bordeaux in 2000 years. Several Gascon 

 villages, the names of which are transmitted by docu- 

 ments of the middle ages, have completely dis- 

 appeared. 



The coasts of the Netherlands, La Vendee, Pata- 

 gonia, and more especially of the Sahara, are among 

 the more important fields of this phenomenon. 



6. Floating Icebergs— Polar Winters. 



As we have already explained, floating icebergs 

 deposit a vast quantity of earthy material at the 

 bottom of the sea. They are, in fact, one of the 

 most powerful agents of transport. As we approach 

 the poles, floating masses of ice are met with. They 

 become larger and more numerous as we advance, 

 and at a high altitude a continuous field of ice 

 stretches before the view, and, no doubt, joins a 

 continent which is also frozen. 



Great danger is incurred in an attempt to pene- 

 trate these regions. Ships are in constant danger of 

 being crushed between the immense masses of 

 floating ice, some of which rise to a height of 40 

 yards above the level of the sea, which corresponds 

 to a submerged thickness of 280 yards. As they 

 advance they gradually melt, and distribute on their 



