318 



Status of the Theory of Isostasy. 



Influence of Datum Surface on the Theory of Isostasy. 



The hypothesis of isostasy stated in general terms is 

 seen to be that the relief of the earth is balanced to a 

 large degree by variations in density in the crust. To 

 subject this hypothesis to mathematical tests certain con- 

 ventional assumptions must be made. If it can be shown 

 that these assumptions involve reasoning in a circle, or 

 if a permissible and alternative change in assumption 

 brings about a radically different solution, then the 



Fig. 2. 



o 



Sea level 



datum 



+ 



CD 



Fig. 2. Assumed relations of elevations to isostatic compensation. 



mathematical evidences of isostasy based on such assump- 

 tions are invalid. If, on the other hand, the assumptions, 

 irrespective of reasonable changes, give consistent solu- 

 tions, then such solutions, although not exactly repre- 

 senting nature, still give the limits within which the 

 actual conditions must vary. 



