34 HAYFORD 



depth I believe that from the observed deflections of the vertical 

 now available the limiting depth of compensation can be derived 

 with reasonable certainty, with an error of less than 25 per cent. 



Thus far this talk has been confined to the direct deductions 

 from the geodetic observations. In this field the speaker en- 

 joys a peculiar advantage in being in unusually close touch 

 with the subject. He has no such advantage with respect to 

 the suggestions which are about to be made on the bearing of 

 these deductions upon some of the greater problems of geology. 

 Nevertheless, the suggestions seem to be desirable in order to 

 indicate some of the important relations of the geodetic investi- 

 gation to other investigations. 



The direct deductions from the geodetic observations, which 

 have been stated, are a safe and strong foundation which can- 

 not be shaken. The superstructure of suggestions which I am 

 about to build upon it is relatively weak and unsafe. Please 

 remember if you do succeed in knocking down the superstruc- 

 ture, that the foundation is still in place and awaiting an abler 

 architect than I am to put a good superstructure upon it. 



The fact is established by this geodetic investigation that the 

 isostatic adjustment brought about by gravity has reduced the 

 stresses to less than one-tenth of those which would exist if the 

 continents and oceans were maintained by rigidity. This gives 

 new and very strong emphasis to the idea that the earth is a 

 failing structure, not a competent structure. The mechanics of 

 the two kinds of structures are very different. 



Geologists, and others who deal with the mechanics of the 

 earth, seem to realize only a part of the time that the earth is a fail- 

 ing structure. Even during the periods of realization it is seldom 

 that one acts upon the supposition that the earth is so utterly in- 

 competent to bear the stresses brought upon it as this geodetic 

 investigation indicates. Let me cite two examples taken from 

 speakers before this Academy and in this room within a year. 



One speaker, in stating the various methods of estimating the 

 age of the earth, referred to the fact that there is no great excess 

 of land surface about the equator as compared with the 

 remainder of the earth. It has been urged that this indicates 



