VOLUME XXII NUMBER 8 



THE 



JOURNAL OF GEOLOGY 



NOVEMBER-DECEMBER 1914 



THE STRENGTH OF THE EARTH'S CRUST 



JOSEPH BARRELL 



New Haven, Connecticut 



PART VII. VARIATION OF STRENGTH WITH DEPTH AS SHOWN 

 BY THE NATURE OF DEPARTURES FROM ISOSTASY 



Introduction and Summary . . . . . . . -729 



SECTION A, PRESENTATION OF THEORY' 



Relations of Loads and Stresses 732 



Stresses Imposed by Harmonic Surface Loads . . . -732 



Modifications Imposed by Long and Large Wave-Lengths . . 736 



Nature of Stresses Imposed by Internal Loads . . . -737 



Nature of Stresses Imposed by Perfect Isostasy . . . . 740 



INTRODUCTION AND SUMMARY 



The first five parts of this article have concurred in showing 

 that the crust is very strong when measured by its capacity to 

 support great deltas, individual mountain ranges, or great internal 

 loads due to irregularities in density not in accord with the topog- 

 raphy. On the other hand, the altitudes of the continents as a 

 whole, or of large sections of the continents, agree with the demands 

 of nearly perfect isostasy. In Part VI it was shown, however, 

 that, although even perfect isostasy threw very considerable stresses 



' Section B, on Applications of the Theory, will be published in the following 

 number of this Journal. The Introduction and Summary apply however to both 

 sections. 

 Vol. XXII, No. 8 729 



