BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 33, pp. 303-316 June 30, 1922 



SOME CONSIDERATIONS TOUCHING OX ISOSTASY * 



BY II. 0. AV00D 1 



(Presented by title before the Society December 20, 1922) 



CONTENTS 



Page 

 Isostasy in geology 303 



Geodetic establishment of isostatic equilibrium ' 304 



Implications of complete isostasy 304 



Difficulties of geologic interpretation 306 



Purpose of present discussion 307 



Superior strength of surface shell in horizontal direction 307 



Spherical continuity of surface shell confining yielding layer 309 



Widespread elastic strain spherically distributed, local failure 310 



Effects of the growth of batholiths 312 



Localized modification of strength in surface shell 313 



Deformation during the erosion-deposition cycle 313 



Seismologic indications of a weak shell 313 



Summary of conclusions 314 



References • 3^5 



Isostasy in Geology 



Since Button's exposition of the principle of isostasy, in 1889, the ad- 

 vance of geologic knowledge has made more and more probable, in a 

 general sense, the reality of isostatic adjustment in the earth. Neverthe- 

 less there has been, and yet is, considerable diversity of opinion amono- 

 geologists regarding the degree of its completeness, the depth at which 

 it is effective, and the mechanisms involved in its accomplishment. Re- 

 cent discussions by Barrell, 1 Leith, 2 and Willis 3 may serve to illustrate 

 this. Moreover, so far as the present writer is aware, no one (except him- 

 self, 4 and he only partially and tentatively) has invoked the principle, on 

 strictly geologic grounds, to explain relations existing among crustal 



* Manuscript received by the Secretary of the Society December 10. 1921. 



This paper is one of a series composing a symposium on isostasy. 

 1 Introduced by William Bowie. 



(303) 



