I9I5.] THE GEOPHYSICAL STANDPOINT. 301 



upon assumptions made to simplify and shorten the computations, 

 which assumptions depart widely from the facts and tend strongly to 

 make the computed stress-differences much smaller than the actual. 

 For example, both Darwin and Love used in their computations 

 hypothetical continents represented by regular mathematical forms 

 in the place of the actual continents with their many irregularities. 

 The maximum stress-difference caused by the actual continents is 

 necessarily much greater than would be produced by the assumed 

 smoothed out, regular, symmetrical continents. 



Similarly, no adequate computations have been made to deter- 

 mine the maximum stress-difference due to the mountains. Darwin 

 computed the maximum stress-difference produced by two parallel 

 mountain ranges, of density 2.8, rising 13,000 feet above the inter- 

 mediate valley bottom, to be 2.6 tons per square inch. Love, for 

 the same mountain ranges, but with isostatic compensation taken 

 into account, computed the maximum stress-difference to be 1.6 tons 

 per square inch. In. this case the computation indicates that the 

 isostatic compensation reduced the maximum stress-difference to 

 but little more than one half what it would otherwise be. Here 

 again both the computed maximum stress-differences have been 

 greatly reduced by substituting hypothetical smoothed-out moun- 

 tains in the place of the actual irregular unsymmetrical mountains. 



To the person who is trying to get a true picture of the present 

 state of stress in the earth, two very important facts are made evi- 

 dent by a comparison of the Love and the Darwin computations. 

 First, the existence of isostatic computation greatly reduces the 

 stress-differences which would otherwise be produced by the weight 

 of the continents and mountains. Second, the depth at which the 

 maximum stress-difference tends to occur is evidently very much 

 less with isostatic compensation than without it. These two con- 

 clusions, based on the differences between the two computations, 

 are apparently reasonably safe even in spite of the same wild as- 

 sumptions on which both the computations were based. 



Note that even a little information as to the distribution of 

 densities — a little information about isostatic compensation — pro- 

 foundly modifies the conclusions as to the state of stress in the earth. 

 It should, therefore, be clear why it was so emphatically stated in 



