Status of the Theory of Isostasy. 303 



terpretation and implying that the surface of the United 

 States is . everywhere almost as closely adjusted to the 

 elevations giving equilibrium as would be the case in an 

 arctic ice pack, where the heights of icebergs and ice floe 

 would depend very closely on the defects of density 

 represented by the masses of ice depressed below sea 

 level. 



How such nice adjustments between elevation and 

 density could harmonize with knowledge regarding the 

 strength of rocks and with the geologic evidence of 

 considerable imperfections in isostasy, the exponents of 

 these views never succeeded in demonstrating. Extreme 

 interpretations frequently fall into error, and under the 

 following topic the adjustments between various lines of 

 evidence will be discussed. 



Interpretations Favoring Isostasy, but Regional and Imper- 

 fect in Character. 



Let attention be turned to the other viewpoint, that 

 which interprets the data as corresponding to a lesser 

 degree of closeness in isostatic adjustment, which regards 

 the crust as strong, the compensation as somewhat 

 irregular, and the depth of compensation as somewhat 

 indefinite. 



Chamberlin pointed out in 1913 that the level bottoms 

 of the old shallow seas showed the surface of the North 

 American continent to have been controlled during pre- 

 vious ages by the position of the sea level over wide 

 areas. Densities could not be supposed to be delicately 

 adjusted to these surfaces controlled by unrelated agen- 

 cies. Chamberlin accordingly maintained that the crust 

 must be both stiff and strong. This argument is of 

 great weight and is seen to imply that the crust is not 

 by any means so pliable and delicately adjusted to small 

 vertical forces as Hayf ord, Reid, and Becker had thought 

 to be implied by the geodetic data. 11 



The present writer made an extensive analysis of the 

 geodetic and geologic data in support of isostasy as a 

 fundamental principle and yet against such close and 

 delicate adjustment as Hayford and some others have 

 thought to exist. This work was published as a series 

 of eleven papers in the Journal of Geology in 1914 and 



11 T. C. Chamberlin, Shelf -seas and certain limitations of diastrophism, 

 Jour. Geology, 21, 523-533, 1913. 



