THE WORK OF THE OCEAN 291 



of the earth, and that the deeper parts of the ocean basin are con- 

 siderably below the mean sphere level, that the name basin 

 seems appropriate. 



The bed of the ocean, like the face of the land, is affected by 

 elevations and depressions, and its deepest parts are about as 

 far below its surface as the highest mountains are above it. 

 If the water were drawn off, so that the bottoms of the ocean basins 

 could be seen, three great features would appear: (1) Extensive 

 tracts of low land, now covered by deep water; (2) other great, 

 but less extensive tracts of higher land, now covered by shallow 

 water; and (3) ridges and peaks of mountainous heights. These 

 three principal divisions may be compared to the plains, plateaus, 

 and mountains of the land, though mountain systems would be 

 less numerous than on land. Furthermore, there would be found 

 great depressions comparable to the great basins of the land. 



Apart from these general features, there is little in common be- 

 tween the topography of the sea bottom and that of the land. If 

 the water were drawn off from the ocean's bed so that it could be 

 seen as the land is, its most impressive feature would be its monot- 

 ony. The familiar hills and valleys which, in all their multitudinous 

 forms, give the land its most familiar features, are essentially 

 absent. A large part of the ocean bottom is so nearly flat that the 

 eye would not detect its departure from planeness, if the water 

 were absent. 



The reason for this profound difference is readily found. The 

 dominant processes which shape the details of the surface of the 

 land are degradational, and though the final result of degradation 

 is flatness (base-level), the immediate result is roughness. In 

 the sea, the dominant processes are aggradational, and tend to 

 monotonous planeness. 



Distribution of marine life. Marine life has been of such im- 

 portance in the history of the earth that the elementary facts 

 concerning its distribution and the principles which control it are 

 here recalled. The distribution of marine life is influenced by many 

 factors, chief among which are temperature and depth of water. Life 

 is more abundant in the warmer parts of the ocean than in the 

 colder, the species inhabiting cold waters are different from those in 



