THE EARTH, A FAILING STRUCTURE. 
65 
sidered that the evidence before them indicates isostatic re- 
adjustment to have occurred. I have elsewhere presented 
some of the geodetic evidence which proves that, at least for 
the United States, there is a rather close approach to the 
isostatic conditions.* 
To the extent that it is proved that isostasy exists, that 
the continents are lighter and the ocean beds denser than 
assumed by Darwin, it is also proved that the stresses within 
the earth are less than his computations would make them. 
At first sight, apparently, it is also proved that there is de- 
creased reason for supposing the earth to be a failing struc- 
ture; but further consideration of the evidence in regard to 
isostasy, combined with geologic evidence, as indicated in 
the following paragraph, shows that, instead of concluding 
that the stresses are small, and that therefore the earth is 
not failing, we should conclude that the earth is failing 
under stresses even smaller than those we had believed to 
exist; that the earth is weaker than we had supposed. 
The geologic evidence is overwhelming that within the 
interval of time covered by the geologic record many thou- 
sands of feet of thickness have been eroded from some parts 
of the earth and have been transported to and deposited 
upon other parts. If isostatic readjustment had not also 
been in progress during this interval, it would be impossible 
for the isostatic compensation to be so nearly complete as 
it is now known to be in and around the United States. By 
isostatic compensation is meant the compensation of the 
excess of matter at the surface (mountains, continents) by 
defect of density below, and of surface defect of matter (val- 
leys, oceans) by excess of density below. Isostatic readjust- 
ment can only take place in two ways: It may take place by 
actual transfer of material beneath the surface. It may 
take place by change of density of matter without transfer 
John F. Hay ford : The Geodetic Evidence of Isostasy. Proceedings 
of the Washington Academy of Sciences, vol. vm, 1900. pp. 25-40; and 
also Geodetic Operations in the United States, 1903-06, a Report to the 
Fifteenth General Conference of the International Geodetic Associa- 
tion, by O. H. Tittmann and John F. Hayford. 
lQ-Bull. Phil, Soo., Wash., Vol. 15. 
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