16 HALF AN HOUR WITH THE WAVES. 



with which the upper surfaces of the rock layers 

 are patterned. 



Keference has already been made to the necessity 

 for some such mighty reservoir of water as the ocean, 

 for the fertilisation of the dry land. The fruitful 

 showers which are constantly falling on the latter 

 all originate in the sea. Before they find their way 

 back again as rivers, what changes have they under- 

 gone ! The fertilisation of the dry land can only be 

 effected at the expense of a certain wear and tear of 

 its surface. This is carried away by rivers and 

 streams into the sea. The insoluble portion is 

 mechanically precipitated, and forms sands and mud- 

 banks the soluble is distributed by tides, currents, 

 &c., through the bulk of sea-water. Now, as the 

 water raised by evaporation from the surface of the 

 sea is absolutely pure, and as that returned to it by 

 rivers is charged with various minerals, it follows 

 that if there were no checks provided, the sea-water 

 would gradually get denser and more saline. The 

 checks are the animal and vegetable life-forms which 

 crowd its waters, which are eternally dying and 

 giving birth within its huge bulk, until the sea- 

 water is, as Dr. Carpenter has well described it, " a 

 kind of weak broth," from the decomposing animal 

 matter dispersed through it. On this " weak broth " 

 the lower forms of life live, sucking? in the nourish- 

 ment by mere contact and absorption. The other 

 species prey on these, and thus the great chain of 

 life extends upwards and onwards. Such minerals 



