THE STRENGTH OF THE EARTH'S CRUST 



293 



whole and for the groups showing the shallowest, deepest, and the 

 most irregular compensation are quoted below. ^ That solution is 

 regarded as nearest the truth which gives the smallest mean value 

 of the squares of the residuals. 



TABLE XIX 



Probable Depths of Compensation 



Group 



Most 

 Prob- 

 able 

 Depth 



Km. 



United States (all observa- 

 tions) 



Group 12 (parts of Minn., 

 N.Dak., S.Dak., Neb., 

 Kan.) 



Group 5 (Mich., Minn., 



Wis.) 



Group 8 (parts of Utah, 

 Nev., Cal.) 



United States (residuals 

 multiplied by 1.327 to 

 compare with Group 8) 



305 



152 

 66 



It is seen that the mean value of the squares of the residuals in 

 group 12 with most probable depth of 305 km. is considerably less 

 than for the United States as a whole, in part no doubt owing to the 

 moderate relief, yet the differences between the residuals in group 

 1 2 for the different solutions is much more pronounced than for the 

 United States as a whole. The number of stations, 36, is large 

 enough so that this can hardly be regarded as accidental. On the 

 contrary, it would appear that for the whole United States the 

 group differences are sufficient to mask in part the accuracy of the 

 mean result of 122 km. and that the depth of compensation within 

 certain groups is more reliable than for the United States as a whole. 



In group 8 with most probable depth of 66 km. the mean value 

 of the squares of the residuals is nearly 50 per cent higher than for 



' 1909, pp- 55-58. 



