ISOSTASY 73 
is reached from the gravity investigation except that the departure 
of compensation from completeness is somewhat greater than 
one-tenth." 
Turning now to Mr. Lewis’ article the present writer is quite 
willing to let the reader decide whether or not Mr. Lewis’ assump- 
tions (p. 626) of over-compensation for all land areas, or of under- 
compensation for all land areas and over-compensation for all 
ocean areas, are arbitrary. 
The preceding parts of this rejoinder have dealt with those 
portions of Mr. Lewis’ article, which are a discussion of the geodetic 
evidence of isostasy. Turn now to the portions of his article in 
which certain geologic evidence is interpreted as being adverse 
to the existence of isostasy. 
On pp. 621-22 Mr. Lewis sets forth the argument that there 
is much geological evidence of horizontal movements in the out- 
side portions of the earth especially in the form of folding, that the 
controlling movements of isostasy are assumed to be vertical 
and hence cannot account for folding, and that the horizontal 
movement or undertow concerned in isostatic readjustment must be 
below the depth of compensation and hence so far below the surface 
as to be very ineffective in producing folding. 
There are two fatal defects in this argument as applied to con- 
tcoverting anything that Hayford believes or has written. 
First, Hayford has already indicated clearly his belief that the 
undertow concerned in isostatic readjustment is above, not below, 
the depth of compensation. In both the figures published in his 
Minneapolis address the undertow is clearly indicated as being 
above the depth of compensation and it is also so indicated in the 
corresponding text. As Hayford puts the undertow comparatively 
near the surface where it is conceded that it would be effective 
in producing folding, the existence of extensive folding is a con- 
firmation not a contradiction of his theory of the manner in which 
isostatic readjustment takes place. It is certainly not fair to 
hold Hayford responsible, either directly or by inference, for any 
theory which someone else may believe which involves an undertow 
™See p. 111 of Special Publication No. ro, of the Coast and Geodetic Survey. 
