THE STRENGTH OF THE EARTH'S CRUST 



66i 



sea-column, as represented by the horizontal lines of the stress 

 diagram. The top of the land-column is balanced only against the 

 negligible weight of the atmosphere and the lateral stress gradient 

 is there highest. The next portion below is balanced against the 



Sea -level 



.P-: 



M 



TTT 



A B C 



Fig. 13. — Diagram illustrating pressure -relations of the crust for marginal 

 portions of the continental shelf and oceanic basin, interpreted as balanced by uni- 

 formly distributed isostatic compensation. Stress-differences are shown by cross- 

 lined diagrams, the pressures being regarded as transmitted hydrostaticaUy. The 

 actual lateral stress-differences, for stresses within the elastic limit, are about one- 

 fourth of the hydrostatic pressures here shown. 



A. Coliunns in isostatic equilibrium. 



B. Relations after base-leveling. 



C. Relations after re-establishment of isostatic equilibrium. 



