THE STRENGTH OF THE EARTH'S CRUST 



33 



resultant is the sum of the individual stress-differences.^ The three 

 waves which have been considered are types which coexist and are 

 superimposed. The total stress which they give would vary from 



Pounds per square inch 



7,000 



1,000 



Kilograms per scjuare cenHmel-er 



■Surface of \he earth 



— F- ^'i~ ~F'— 



Lifhosphere ^' — -TT^r^ 



okm. 



Ashhenosphere 



Centro sphere 



Fig. i8. — Stress-curves for harmonic waves on an earth elastically competent 

 throughout, the waves representing departures from isostasy in the United States 

 as given by analyzing the geodetic data into the following harmonic waves: 



A, wave-length i6o km., amplitude o. 120 dyne = 2,440 m. of rock. 



B, wave-length 600 km., amplitude 0.080 dyne = i,oi5 m., of rock. 



C, wave-length 2,800 km., amplitude 0.042 dyne = 380 m. of rock. 

 D is the sum of A, B, and C. 



E, wave-length 400 km., amplitude 0.366 dyne = 4,000 m. of rock (from the 

 Pacific Ocean). 



F', curve of strength suggested by geodetic evidence from the United States. 



F", curve of strength suggested by geologic evidence from various parts of the 

 world. 



complete neutralization up to their sum as a possible maximum. 

 Curve D represents such an addition of A, B, and C, Fig. 18. There 

 are reasons why this curve may be taken as a fairer representation 

 of the maximum stress conditions under the United States than 



Scientific Papers, II, 492. 



