BULLETIN OF THE GEOLOGICAL SOCIETY OF Al^^^ ^^ Cq/* 



Vol. 31, pp. 247-302, PLS. 8-13 JUNE ^fo, 1920 "^* <%« 



SEP ^1 iQon 



00- 



DISCOIDAL STEUCTUEE OF THE LITHOSPHEEE ' 



BY BAILEY WILLIS 



(Presented in abstract before the Society December 21 , 1918) 



CONTENTS 



Page 



Advanced summary 247 



lutroduction 250 



Thesis 250 



Essential concepts 250 



Mechanical state of the isostatic shell 252 



Efifect of pressure 252 



Effect of heat 261 



Summary as to the mechanical state 265 



Isostasy as a working hypothesis 266 



Development of the discoidal hypothesis 274 



Distribution of heterogeneous masses 274 



Departures from average densities 280 



Direction of elastic stress 280 



Effects of isostatic stress on foliation 284 



Distribution of foliation 288 



Suboceanic conditions of foliation ^. 291 



Disks and interdisks 9^2 



Suboceanic structure 294 



Problem and premises 294 



Hypothetical alternatives 294 



Origin of ocean basins 295 



Explanation of plates oqq 



Advanced Summary 



The following discussion seeks to determine inductively the structural 

 character of the lithosphere at depths beyond the reach of observation. 



The mechanical state of the outer shell of t]ie lithosphere is discussed 

 on the basis of A dams^ experiments with rocks under confining pressures, 



' Manuscript received by the Secretary of the Society December 15 1019 

 Entered in printed program under the title "Structure of the Pac'ific ranges of Cali- 

 fornia and included in outline in the oral presentation of that topic, but subsequently 

 expanded to the present article. ^ equeuny 



XVII— Bull. Geol. Soc. A.m., Vol. .^1, 1010 ,247^ 



