18 



EARTH FEATURES AND THEIR MEANING 



outline perpendicular to this face is imperfectly heart-shaped or 

 like a flattened " peg top." 



The flooded portions of the present continents. We are accus- 

 tomed to think of the continents as ending at the shores of the 



oceans. If, however, we 

 are to regard them as 

 platforms which rise 

 from the ocean depres- 

 sions, their margins 

 should be considerably 

 extended, for a sub- 

 merged shelf now prac- 

 tically surrounds all the 

 continents to a nearly 

 uniform depth of 100 

 fathoms or 600 feet. 

 The oceans thus more than fill their basins and may be thought of 

 as spilling over upon the continents. In Fig. 7, the submerged por- 

 tions of the continents have been joined to those usually represented, 

 thus adding about 10,000,000 square miles to their area, and giving 

 them one third, instead of one fourth, of the lithosphere surface. 



The floors of the hydrosphere and atmosphere. The highest 

 altitudes upon the continents and the profoundest deeps of the 



S S 



FIG. 7. The continents with submerged portions 

 added (after Gilbert). 



FIG. 8. Diagram to indicate the altitude of different parts of the 

 lithosphere surface. 



ocean are each removed about 30,000 feet, or nearly 6 miles, 

 from the level of the sea. In comparison with the entire surface 

 of the lithosphere, these extremes of elevation represent such 

 small areas as to be almost inappreciable. Only about ^ of the 



