372 THE BOTTOM OF THE SEA. 



with the coast-line, the dunes, and the lagoons, con- 

 stitute the littoral apparatus. *' 'J^hey combine to 

 form a very decisive line of demarcation between the 

 region of storms and agitation outside the sea, and 

 the abode of peace within the laud."* 



The coast-line, in some cases, may become a 

 barrier which completely separates the waters of a 

 gulf from those of the sea. But even when the coast 

 presents no hollow for the collection of the water, 

 salt lakes or lagoons may be formed if a line of rocks, 

 visible or not above water, should exist at a certain 

 distance from the shore, and form a bar to the sand 

 or other stuff that may be washed up by the sea. 

 The lagoon may retain one or two communications 

 with the sea, in tlie shape of channels, or it may 

 become completely enclosed. 



Marine jponds are deep lagoons ; they are numerous 

 on the coast of France. That of Thau, near Cette, is 

 one of the most remarkable. If a lagoon entirely 

 separated from the sea does not receive any stream 

 of water, it dries gradually, and increases in saltness. 

 When it receives a river, its saltness diminishes. In 

 any case, the creatures which it feeds are modified 

 according to the changes in the composition of the 

 water. Thus, the lagoons of Finland are inhabited 

 by freshwater animals, and also by a kind of shrimp 



* Elie de Beaumont, Ler^ons de Geologie Pratiqiie. 



