ISOSTASY 563 
conclusions from the geodetic evidence than those given by Hayford. 
A careful reading of the article shows, however, that Lewis has 
simply suggested that other conclusions are possible. Hayford 
believes that the arguments in Mr. Lewis’ article which are based 
on geological evidence are essentially weak and in part erroneous. 
This rejoinder is an attempt to show briefly some of the basis 
for the writer’s beliefs as expressed in the preceding paragraph. 
In the first part of this rejoinder practically all of the evidence 
cited was available to Mr. Lewis before he wrote his paper. In 
the latter part some new evidence, from gravity observations, is 
utilized which has not heretofore been accessible to Mr. Lewis 
but which is now accessible to all interested persons. 
Mr. Lewis claims that Hayford made a fundamental error in 
that ‘‘the most probable depth was calculated on the assumption 
of completeness. If the assumption of completeness was wrong, 
the depth of compensation which would appear most probable 
would not be the true depth of compensation but a depth which 
would counteract the effect of the wrong assumption in regard to 
the completeness” (p. 612). Referring to the same matter, on 
p. 625, Mr. Lewis writes, “It is believed that Hayford made an 
error in determining the degree of completeness of compensation 
which invalidates his conclusions, for he assumed complete com- 
pensation in calculating the depth and then used this depth to 
calculate the degree of completeness.’ In contrast to the published 
conclusions by Hayford,’ Mr. Lewis writes in connection with the 
same matter (p. 612), ‘‘We are forced to conclude that, from the 
geodetic evidence alone, neither the depth nor the degree of com- 
pleteness of isostatic compensation can as yet be considered settled.” 
Recur for a moment to Mr. Lewis’ statement (p. 612), that 
“Tf the assumption of completeness was wrong, the depth of com- 
pensation which would appear most probable would not be the 
true depth of compensation but a depth which would counteract 
the effect of the wrong assumption in regard to completeness.” 
This statement involves in itself an assumption which is absolutely 
essential to Mr. Lewis’ whole argument, namely, that the counter- 
tSee The Figure of the Earth and Isostasy, pp. 164-66, 175, and Supplementary 
Investigation, pp. 59, 77- 
