CHAPTER XVI 

 CONTINENTS; OCEANS 



210. The Relation of Land and Water. If we could 

 view the earth from a great distance, we should see vast 

 stretches of level water broken by smaller areas of uneven 

 land. The water is all one body, though separated into 

 somewhat distinct parts called by different names. The 

 land masses, or continents, are gathered into two groups 

 which almost meet around the north pole. Two thirds of 

 all the land is in the northern half of the globe. The 

 continents are like the tops of great elevated blocks of the 

 earth's crust. Some islands are parts of the same block as 

 the neighboring continent, but many are the summits of 

 ocean mountains and volcanoes. 



To the east of the United States, the continental block 

 extends far into the Atlantic Ocean. For a great many miles 

 from the coast the water is shallow; that is, it is six hun- 

 dred feet deep or less. It then suddenly becomes several 

 thousand feet deep. The place where the water deepens 

 is the eastern edge of the continental block. The portion 

 of this block covered with shallow water is the continental 

 shelf. Newfoundland, Cape Breton Island, Martha's Vine- 

 yard, and Nantucket are elevations in the continental shelf. 



Sand and mud brought from the land are all the time 

 being deposited upon the continental shelf. As the sedi- 

 ment collects, it adds little by little to the extent of the 

 land, just as the rock waste brought by a river sometimes 

 forms a great delta at the mouth. A slight elevation of 

 the continental shelf may bring above the surface of the 

 water many acres of low barren plain and thus extend the 



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