302 Status of the Theory of Isostasy. 



of this hypothesis have been discussed by the present 

 writer. 6 



Becker, accepting Hayford 's results enthusiastically, 

 has even gone beyond him in interpreting the supposed 

 perfection of isostasy. Becker placed such great reli- 

 ance upon Hayford's first determination of the depth 

 of isostatic compensation, 114 kilometers, that he based 

 a test of the age of the earth and the part of radio- 

 activity in the crust upon this figure. 7 Bowie has since 

 shown how indefinite is this depth of compensation. 

 Hayf ord regarded the gravity anomalies as due to out- 

 standing loads representing departures from isostasy. 

 Gilbert showed, however, that isostasy might be perfect, 

 and still, if the compensation occurred at various depths 

 and especially if light and heavy masses were balanced 

 against each other in the same vertical column, very 

 considerable anomalies of gravity would appear. There- 

 fore, Gilbert held that it remained to be proved to what 

 degree the anomalies represented departures from per- 

 fect isostasy. 8 Barrell developed independently the same 

 conclusion as Gilbert, but going farther, sought the 

 answer as to whether the anomalies did result from mere 

 vertical irregularity of compensation or from real de- 

 partures from isostasy. By devising criteria depending 

 on the character of the anomalies, as well as by various 

 kinds of corroborative testimony, the conclusion was 

 reached that the anomalies do represent in greater part 

 such loads, positive or negative, and furthermore that 

 the masses and resultant stresses were much larger than 

 Hayford had supposed them to be. 9 Yet Becker in 1917 

 assumes without any proof or even adequate discussion 

 that the anomalies result from mere vertical variations 

 in the distribution of compensation, and do not measure, 

 except to an insensible degree, real departures from isos- 

 tasy. 10 Becker stands thus as the extreme exponent of 

 perfect isostasy, going even beyond Hayford in his in- 



6 Joseph Barrell, Science, new ser., 29, 257-260, 1909; Jour. Geology, 22, 

 672-683, 1914. 



7 G. F. Becker, Age of a cooling globe in which the initial temperature 

 increases directly as the distance from the surface, Science, new ser., 27, 

 227-233, 1908; also in later publications. 



8 G. K. Gilbert, Interpretation of anomalies of gravity, U. S. Geol. Survey, 

 Prof. Paper 85-C, 1913. 



9 Joseph Barrell, Influence of variable rate of isostatic compensation, Jour. 

 Geology, 22, 209-236, 1914. 



10 G. F. Becker, Isostasy and radioactivity, Bull. Geol. Soc. Amer., 26, 187, 

 1915. 



