THE STRENGTH OF THE EARTH'S CRUST 



JOSEPH BARRELL . 



New Haven, Connecticut 



PART VII. VARIATIONS OF STRENGTH WITH DEPTH AS SHOWN 

 BY THE NATURE OF DEPARTURES FROM ISOSTASY 



SECTION B, APPLICATIONS OF THE THEORY 



Geodetic Evidence as to Limiting Heights and Wave -Lengths . 27 



Measurements of Strength by Maximum Loads 27 



Harmonic Loads with Short Wave-Lengths 28 



Maximum Loads for Mean Wave-Lengths 29 



Departures from Isostasy of Large Wave-Lengths 30 



Relations of Actual Stresses to the Sum of Harmonic Waves 32 



Geologic Suggestions as to Magnitudes of Crustal Stresses 35 



Submarine Geanticlines and Geosynclines 35 



The Niger Delta 38 



The Existing Continental Ice Sheets ;^8 



Accordance of Geologic with Geodetic Evidence 40 



Adjustment of Loads to the Distribution of Strength ... 40 



Character of the Curve of Strength 42 



GEODETIC EVIDENCE AS TO LIMITING HEIGHTS AND 

 WAVE-LENGTHS 



Measurements of strength by maximum loads. — In the course of 

 geologic time the internal forces of igneous intrusion and tangential 

 compression, the external forces of erosion and sedimentation, have 

 tended to strain the crust to its Kmits of strength, and the degree 

 of isostasy w^hich exists constitutes a measure of those limits. 

 Small loads of large wave-length and large loads of small wave- 

 length will tend to rise to maxima which may be used in connection 

 with the theory of distribution of stress, as considered in Part VII, 

 Section A, to give an approximate idea of the limits and distribution 

 of strength in the crust. 



The problem is to find the maximum vertical load and its rela- 

 tion to wave-length acting over areas which may be regarded as 



27 



