THE DOCTRINE OF ISOSTATIC COMPENSATION 691 



Hayford's Figures Analyzed with the Idea or Compensation Eliminated 

 Deflections Corrected for Topography to Find Attraction of Hidden 



Masses 

 Distribution of Residuals in Excess of 50" of Arc 

 Distribution of Residuals in Excess of 35" of Arc 

 General Conclusion as to General Law of Distribution of Anomaly of 



Gravity 

 Criticism of Hecker's Determinations of Gravity over the Open Sea 

 Helmert's Claim that Gravity Is Nearly Constant over the Deep Water 



of the Ocean 

 Hecker's Grouping of His Data Objectionable in That It Tends to Efface 



Significant Local Anomalies 

 Hecker's Revision of His Data after the Black Sea Cruise 

 Hecker's Figures in General Indicate Large Anomalies of Gravity above 



Submerged Escarpments and Near Where Seaquakes Have Been 



Felt 



INTRODUCTION 



A rigid versus a plastic earth shell. — The doctrine of isostasy is 

 an expression of disbelief that the outer shell of the lithosphere is 

 sufficiently strong to support the protuberances upon its surface. 

 An added idea is that, since it is a failing structure, it is sensitive 

 to surface transfers of rock material and responds with a subsidence 

 beneath freshly loaded areas and with corresponding elevation 

 within denuded districts. It should never be forgotten that this 

 theory was conceived at a time when belief in a liquid interior of our 

 planet was general, and that its adjustment to the modern view of 

 a rigid earth is a matter of the last decade only. Probably the 

 fact which more than any other has compelled geologists to consider 

 the question of possible high plasticity within the earth's outer 

 shell is the great thickness of shallow-water deposits that have 

 been laid down in geosynclines. Although to some extent the recent 

 recognition of the large importance of continental deposits within 

 ancient sedimentary formations has required a modification of 

 earlier assumptions, there is still a call for some explanation of the 

 apparent balance which has been maintained between subsidence 

 and the quantity of deposited material within the basins of sedi- 

 mentation. Obviously two contrasted hypotheses may be offered. 

 Upon the one hand, it may be assumed that the adjustments in 



