VOLUME XXII NUMBER 4 



THE 



JOURNAL OF GEOLOGY 



MAY-JUNE 191 4 



THE STRENGTH OF THE EARTH'S CRUST 



JOSEPH BARRELL 



New Haven, Connecticut 



PART IV. HETEROGENEITY AND RIGIDITY OF THE CRUST AS 

 MEASURED BY DEPARTURES FROM ISOSTASY 



Introduction and Summary . 289 



Variable or Constant Depth of Compensation .... 291 

 Departures from Isostasy Sustained by Rigidity in the Zone of 



Compensation 296 



Interpretation of Deflection Residuals in Terms of Masses . 297 



Maximum Loads Indicated by Anomalies 302 



Further Geodetic Work Needed for Geologic Problems . . 313 



INTRODUCTION AND SUMMARY 



In Part I were examined certain geologic tests of the strength of 

 the crust; in Part II the geodetic evidence in regard to the effective 

 areal Kmits of rigidity; in Part III the influence of variable vertical 

 distribution of density. All three lines of investigation converge 

 toward showing the rigidity of the outer crust — the zone of isostatic 

 compensation — to be such that very considerable stresses can be 

 carried over areas whose radii range between 100 and 300 km. 

 There arise to be considered next the following problems: first, 

 the variability in depth of compensation and its influence; second, 



Vol. XXII, No. 4 289 



