424 WILLIAM BOWIE 



Professor Hayford stated that the anomalies or deflections of 

 the vertical, resulting after the application of the correction for 

 isostatic compensation as well as for the topography, would be an 

 indication of the extent to which the conditions postulated would 

 not be true. 



Professor Hayford should have stated that the compensation 

 departed from perfection only 10 per cent locally, for there is no 

 indication that there is a departure of 10 per cent from the perfect 

 state for the whole country. Some of the anomalies were positive 

 and others negative and these tend to balance for the whole area. 



Several tests were made by Professor Hayford to show the 

 result of other methods of vertical distribution of the isostatic 

 compensation than the one of uniformity. If the isostatic compen- 

 sation is uniformly distributed through a stratum 10 miles thick, 

 he found the most probable depth for the bottom of this stratum 

 to be 40 miles. If the isostatic compensation is distributed with 

 respect to depth, according to the law postulated by Professor T. C. 

 Chamberlin, the most probable value of the limiting depth is 193 

 miles. The method of distribution of the compensation by Pro- 

 fessor Chamberlin's method is given on pages 159 and 160 of The 

 Figure of the Earth and Isostasy from Measurements in the United 

 States. This is the first report 1 on the deflection of the vertical and 

 isostasy. In regard to the Chamberlin method, Hayford said: "It 

 is not possible to ascertain whether this compensation is more 

 probable than the solution G compensation, uniformly distributed 

 from the surface to a depth of 70.67 miles, since the two sets of 

 computed deflections agree so closely that their differences are much 

 smaller than the accidental errors." 



When the investigations of gravity and isostasy were under- 

 taken, it was concluded that the compensation should be distrib- 

 uted uniformly to a depth of 113.7km., which was the depth 

 determined by Hayford in his first investigation of the deflection 

 of the vertical and isostasy. The uniform distribution was adopted 

 because it made easier the preparation of the tables with which the 

 computation of the effect of the isostatic compensation was made. 

 It was also believed that this method of distribution was as probable 



1 Special report (not numbered) of the Coast and Geodetic Survey, 1909. 



