316 Statu? of the Theory of Isostasy. 



with some observations not closely. On the average, as 

 previously stated, it accounts for nine-tenths of the 

 deflections and gravity abnormalities to be explained, 

 leaving only one-tenth as residuals and anomalies. It is 

 true, as Hobbs states, that near masses have preponder- 

 ant effects, and such near masses not in agreement with 

 isostasy account for a considerable part of the deflection 

 residuals and gravity anomalies; The data are as yet 

 too coarse to measure many of the masses, but the writer 

 has tested the matter for certain regions and reached a 

 first approximation. 22 It would appear that the theory 

 of isostasy has more than justified itself, and that, as a 

 result of its application, we are coming to know some- 

 thing, instead of nothing, concerning the distribution of 

 mass beneath the earth's surface. 



Hobbs states that Hayford's explanation of anomalies 

 rests on an assumed systematic regularity as contrasted 

 to local irregularity in distribution of mass, and implies 

 that the residuals are made to disappear by a process of 

 averaging. It may be replied that the test by the method 

 of least squares is by no means a process of causing 

 residuals to disappear by averaging. The process, on 

 the contrary, is one of making the individual residuals 

 become small by finding that law by which calculation 

 and observation come nearest to agreement. Hobbs's 

 argument implies that a small local mass of high posi- 

 tive or negative density could be placed near each station 

 so as to give the observed deflection or intensity of 

 gravity at that point without affecting the other stations, 

 in this way simulating the influence of systematic iso- 

 static compensation. "When the number of stations is 

 considered, it is seen that the appropriate location of 

 such local masses would call for an amount of creative 

 design to delude mankind comparable to that sometime 

 theological argument that fossils were created to mislead 

 those who should be guilty of undue prying into the 

 secrets of nature. 



In 1917 W. D. MacMillan contributed a paper entitled 

 < ' On the hypothesis of isostasy. ' ' 23 This is a brief paper, 

 for one covering so large a subject. Its attitude is that 

 of skepticism toward any specific form of isostatic theory 

 and of destructive criticism toward the one employed by 



22 Joseph Barrell, The strength of the earth's crust, Jour. Geology, 22, 

 302-314, 441-468, 537-555, 1914. 



23 W. D. MacMillan, Jour. Geology, 25, 105-111, 1917. 



