610 HARMON LEWIS 



compensation at depth zero under ocean areas. It was found that 

 these assumptions were not as close to the facts as the assumption 

 of complete compensation at the depth of 76 miles under both 

 land and ocean. In discussing the C-solution Hayford says: 1 



It follows, moreover, that it is an isostatic compensation of the separate 

 topographic features of the continent, not a compensation merely of the conti- 

 nent as a whole. In solution A 2 it is a compensation of the separate features 

 which is assumed. An inspection of the numerical values of the computed 

 topographic deflections, and of the deflections computed with isostatic com- 

 pensation considered shows that merely to have assumed the continent as a 

 whole to be compensated, not its separate topographic features would have 

 given a solution resembling solution C much more closely than solution A. 3 



A very vital step in Hayford's work is his determination of the 

 degree of completeness of compensation. As this is one of the 

 principal points to be criticized, his method will be explained in 

 detail in connection with the criticism. Suffice it to say here that 

 he concluded that the isostatic compensation is on an average nine- 

 tenths complete. 



CRITICISM OF HAYFORD'S WORK 



Hayford certainly showed that there is some sort of isostatic 

 compensation; but he did not fully consider all possibilities as to 

 the nature of this compensation. The exact nature of isostatic 

 compensation for any place is determined by three factors, (1) depth 

 of compensation, (2) distribution of compensation, and (3) degree 

 of completeness of compensation. Hayford considered all possible 

 depths of compensation and several distributions of compensation ; 

 but all of his solutions involving isostatic compensation were made 

 on the assumption that the compensation is complete. This was a 

 purely arbitrary assumption on Hayford's part since he gave no 

 reason whatever for believing at the outset that compensation is 



1 Quoted from p. 169 of 1909 report. 



2 Solution A was made on the assumption that compensation is complete at depth 

 zero over both land and sea. This solution turned out to be nearer the truth than 

 solution C. 



3 It should be noted that the assumption of complete compensation under ocean 

 areas with no compensation under continents is not equivalent to a compensation of 

 the continents as a whole with respect to the oceans, but only to a compensation for 

 the part of the continents below sea level. 



