COMPOSITION OF OCEAN WATERS 



273 



nishes the great fishing banks of the earth, sueh as the 

 Grand Banks of Newfoundland and those around Iceland 

 and the Lofoten Islands, where fishermen for ages have 

 obtained vast supplies of fish. There is no equal area of 

 the earth where the life is so varied and the struggle for 

 existence so great as on these shallow continental borders. 



CONTINENTAL SHELF. 

 A model showing the sea floor off the coast of Southern California. 



Here the mud and sand brought down by the rivers is 

 spread out and the sedimentary rocks formed. It is the 

 elevation of this shelf which has formed the low-lying 

 coastal plains which border many of the continents. 

 There is good reason to believe that the deep floors of the 

 sea have never been raised into dry land, and that the 

 vast extent of sedimentary rocks which make up the larger 

 portion of the land has almost all been laid down in re- 

 gions which were at the time continental shelves. 



127. Composition of Ocean Waters. Experiment 122. Into 

 a dish of fresh water put a demonstration hydrometer or stick such as 



