436 WILLIAM BOWIE 



It is interesting to note that, in the deflection of the vertical 

 investigations, depths of compensation were determined for a num- 

 ber of groups, in addition to a depth for the whole country using 

 all the stations as one group. 1 When we use the groups which are 

 in mountainous regions and give the value of the depth of compensa- 

 tion derived from each group the same weight, it is found that the 

 depth of compensation, as derived from deflections of the vertical 

 data, for stations in mountainous regions only, is 97 km. It is 

 rather remarkable that practically the same depth should be ob- 

 tained from such widely different geodetic data. It is believed 

 that the mean of these two values, or 96 km., is about the best 

 value that is available at present from all geodetic data. As in 

 other tests made during the investigation of gravity and isostasy, 

 it was necessary to assume that all of the anomalies were due to the 

 erroneous depth of compensation when the derivation of the most 

 probable depth was made. This necessarily places some uncer- 

 tainty in the depth of compensation, although it is believed that 

 the uncertainty due to that cause is moderate in amount. It is 

 probable that the best depth of compensation which will be derived v 

 from more geodetic data will be somewhere between 80 and 130 km. 

 This, of course, is on the theory that the compensation is distributed 

 uniformly from the surface or from sea-level to the depth of com- 

 pensation. 



The writer does not believe, as was stated earlier in this paper, 

 that the compensation is distributed locally and uniformly to the 

 depth of compensation. It is possible that the compensation may 

 be distributed by some other method. It is probable that there 

 is no method of distribution that is general, that is, applicable to 

 each local area in the country. It seems to be most probable that 

 the compensation varies from place to place and that the greater 

 portion of the compensation may be near the surface in one place 

 and lower down in another, or that it may be distributed through- 

 out a considerable depth with varying amounts at different depths. 



A computation was made, but the results of this do not appear 

 in Special Publication No. 40, which showed the depth of the disk 



1 See Supplementary Investigations in 1909 of the Figure of the Earth and Isostasy, 

 p. 58. 



