Uplift and Subsidence. 11 



topography and isostatic compensation. I simply raise 

 the point here because attempts have been made to show 

 that the isostatic results are made somewhat unreliable 

 by some other datum not having been adopted._ The 

 principal reason why this subject should be considered 

 is that the question of the percentage of completeness of 

 compensation is involved in it. You will notice that I 

 have not previously made any statement in regard to the 

 percentage of completeness of compensation. I have 

 simply shown that the isostatic reductions reduce the ano- 

 malies to a certain per cent of what they would be if the 

 earth were rigid. It is difficult to interpret the results 

 in terms of mass. 



The actual distribution of compensation cannot he proved 

 mathematically. 



The statement was made by McMillan, in his article on 

 the ^^ Hypothesis of Isostasy" (Journal of Geology, 

 February-March, 1917), that 



' ' From a purely mathematical point of view any set of a finite 

 number of observations of the intensity and direction of gravity 

 can be satisfied, not approximately, but exactly in infinitely many 

 ways by a proper distribution of the density of the earth. ' ' 



Speaking mathematically, this statement is justified, 

 but any distribution of the densities in the earth that is 

 not general in its application, which would exactly elimin- 

 ate the anomalies of the deflections of the vertical and of 

 the intensity of gravity, would be so artificial as not to 

 be at all reasonable. It seems to be logical to assume 

 that the only reasonable hypothesis regarding the distri- 

 bution of the densities in the outer portion of the earth is 

 one which will be very general in its application. We 

 cannot accept methods of distribution which are designed 

 simply to eliminate the anomaly by having one distribu- 

 tion at one gravity station, another distribution for a 

 second station, and so on throughout the list of stations. 



Prediction as a test of isostasy. 



The results of the investigation into the theory of 

 isostasy have been very striking and this is brought out 

 clearly in a recent article entitled '^ A Brief review of the 

 evidence on which the theory of isostasy is based'' by Col. 



