412 Jones — Review of Chamberlin's Groundwork 



Bearings on Isostasy. 



It is, of course, an evident fact as Chamberlin states 42 

 that: "a liquid earth should be an ideal example of 

 perfect isostasy in the highest sense — that is, isostasy in 

 perfect horizontal as well as vertical adjustment," but 

 is the further statement that: "the earth's crust, as it 

 began to form, should have inherited this quality in full 

 perfection" 43 true in its implications? This statement 

 implies that any subsequent deformation of the crust 

 would merely act as an upsetting influence to this perfect 

 isostatic state. Now perfect isostatic adjustment in a 

 "horizontal" direction does not mean, of course, perfect 

 leveling of the surface unless, of course, in the case of a 

 crustified earth, the crust is of uniform composition and 

 thickness in a worldwide sense. Such an ideal state may 

 possibly have obtained immediately after crustification. 

 But this thin crust must have been very weak and readily 

 subject to disruption. Fragmentation would involve 

 engulfment, the outpouring of more basic materials and 

 their solidification would then introduce heterogeneities 

 of density in the crust and those portions so weighted 

 down would seek their level of adjustment. The broader 

 the area so weighted down, the more perfect would that 

 adjustment be. In fact, the suggestion has been made 

 by Willis and Barrell 44 that the ocean basins owe their 

 origin to such a process as this. 



A state of perfect isostasy is, under this view, possible 

 only within the limitations imposed by the strength, of 

 the earth's crust and that strength becomes small for 

 broadly distributed loads and great for more constricted 

 loads and so an almost perfect state of isostatic adjust- 

 ment must prevail as between oceanic depressions and 

 continental areas. There is no antagonism here between 

 isostasy and diastrophism. The strength of the earth's 

 crust merely interposes as a barrier to perfect adjust- 

 ment. Diastrophism is the expression of the final over- 

 throw of the crustal resistive power and this overthrow 



42 Op. tit., p. 209. 



43 Idem., p. 209. 



44 Joseph Barrell &' Others: The Evolution of the Earth, 1920, pp. 39-43. 

 Bailey Willis: The Discoidal Structure of the Lithosphere, Bull. Geol. 



Soc. Am., vol. 31, p. 298, 1920. 



