THE SURFACE OF THE EARTH 161 



earth is one continuous body, it is only for convenience 

 that different parts have received different names. 

 In area the ocean covers about three-fourths of the 

 earth's surface. Its average depth is about two and 

 one-half miles. If all irregularities of the earth's 

 crust were smoothed off, the water would cover the 

 entire earth's surface to a depth of nearly 9,000 feet. 

 The ocean is continually at war with the land. Its 

 main work, with the aid of rain and streams, is to 

 carry the land into the sea. Charlotte P. Stetson has 

 expressed it thus : 



I am the Sea ! I hold the land 

 As one holds an apple in his hand; 

 Hold it fast with sleepless. eyes, 

 Watching the continents sink and rise. 

 Out of my bosom the mountains grow, 

 Back to its depths they crumble slow. 

 The iron cliffs that edge the land 

 I grind to pebbles and sift to sand; 

 I comfort the earth with rains and snows 

 Till waves the harvest and laughs the rose. 

 Flower and forest and child of breath 

 With me have life without me death. 

 The earth is a helpless child to me. 

 I am' the sea ! 



The ocean may never entirely complete its task. 

 Water is held on the surface of the earth by the inter- 

 ior heat which allows it to penetrate only to a certain 



