MOVEMENTS AND DEFORMATIONS 357 



tinents. The reasons for this will be set forth later. If the ocean 

 basins and the continental platforms, respectively, be regarded as 

 the surfaces of great segments of the earth all of which are crowd- 

 ing toward the center, the stronger and heavier segments may be 

 conceived to take precedence, squeezing the weaker and lighter 

 ones between them. The consequent swelling up of the lighter 

 segments accounts for the relative protrusion of the continents. 



The area of the more depressed segments is almost exactly twice 

 that of the protruding ones, if we count the 10,000,000 square 

 miles now covered with shallow water as parts of the continental 

 platforms. Roughly approximated in millions of square miles, 

 the major depressed segments are as follows: The Pacific 60, the 

 Indian 27, the South Atlantic 24, the North Atlantic 14, leaving 

 8 for minor depressions. The elevated segments are the Eurasian 

 24, the African 12, the North American 10, and the South American 

 9, leaving 10 for the minor blocks. 



The downward movement of the master segments and the 

 crowding of the smaller and lighter segments between them involves 

 deformations of the latter. Those that spring from the deeper, 

 more massive crowdings affect the continental platforms generally, 

 or at least broadly, while the crowding of the more superficial 

 parts affects the continents more locally. The great plateaus lie 

 chiefly at angles in the great segmental movements, where special 

 crowding naturally arises. It is obvious that on the borders of the 

 continental segments there would be special bowings, and this 

 tallies with the archings common on border tracts, even when no 

 folding takes place. The shell of the earth is free at the surface, 

 and as a result, folding and faulting are the modes of easiest accom- 

 modation, while in the deeper parts which are under great pressure, 

 the mass must be deformed throughout. 



The periodicity of the movements is assigned to the rigidity of 

 the thick, massive segments which must be deformed to accomplish 

 a readjustment. Because of this rigidity, stresses may accumulate 

 for a period until they come to equal the resistance opposing them, 

 after which a further increase of the stresses brings on a yielding 

 and forces a readjustment. When masses, under stress, once 

 begin to yield in the direction of the free surfaces, their attitudes 



