320 



Status of the Theory of Isostasy. 



and +6,000 feet measured with respect to sea level, these 

 being the elevations by which MacMillan illustrates his 

 argument. Under the theory of isostasy each column has 

 the same mass. 



The unknown to be sought is the depth of compensa- 

 tion, h l9 under the assumption of a uniform distribution 

 of the compensation, and the test of the solution is to 

 see if the calculated deflections of the vertical and the 



«-6,ooo.feer. 

 Sea level. 



-9,000. 



Depth Of 

 co mpensarioi 



Fig. 3. Diagram to show relations of elevations to defects in density in 

 accordance with the hypothesis of uniform vertical distribution of isostatic 

 compensation through a constant depth of crust. 



intensities of gravity are by this ascertained depth of 

 h± made to agree closely in a great mass and variety of 

 data with the observed values. As a matter of fact, 

 Hayford and Bowie's results, as is well known, reduced 

 the discrepancies on the average to one-tenth of the effect 

 of the topography without compensation. What, then, 

 would be the effect of changing the datum plane from 

 sea level to the mean surface of the geoid, 9,000 feet 

 below 1 Will such change give another value to the depth 

 of compensation or to the deflection calculated from that 

 depth? 



