574 JOHN F. HAYFORD 
situated entirely below the depth of compensation. Mr. Lewis 
apparently believes such a theory. 
Second, the movements which produce isostatic readjustment 
are necessarily horizontal not vertical. If two adjacent columns 
of the same horizontal cross-section extending from the surface 
to the depth of compensation have different masses the readjust- 
ment to perfect compensation must involve a transfer of mass out 
of one column, or into the other, or from one to the other. In 
any case the transfer must be a horizontal movement, though it 
may be incidentally accompanied by a vertical movement. Hay- 
ford has already shown in print more than once that he understands 
that vertical movement alone does not produce isostatic readjust- 
ment. Moreover, a careful reading of his Minneapolis address 
will certainly show that he believes that the total amount of material 
moved horizontally during isostatic readjustment, and especially 
the total number of ton-miles of such movement, is vastly in 
excess of the corresponding quantities concerned in the vertical 
components of the movement which takes place. Hence the 
folding and other abundant evidence of past horizontal movements 
observed by geologists confirm Hayford’s hypothesis as to the 
manner in which isostatic readjustment takes place, instead of 
conflicting with it as Mr. Lewis’ article would lead one to think. 
In contrast to the paragraph at the top of p. 623 of Mr. Lewis’ 
article in which he claims that “the theory of isostasy does not 
explain the apparently heterogeneous relation of uplift and sub- 
sidence to erosion and deposition,” the writer respectfully requests 
that certain parts of his Minneapolis address be considered in 
which it is set forth at some length that the movements concerned 
in isostatic readjustment at a given time and place are probably 
a function not simply of the facts at that time and place but also 
of the past facts there and of the current facts at many other 
places, some at a considerable distance, perhaps hundreds of miles 
away. If this be true, one should not expect to find a fixed relation 
of uplift and subsidence at any given point or time to the erosion 
or deposition in progress at that point at that time. Why does 
Mr. Lewis ignore this contrast ? 
So too, when one reads Mr. Lewis’ statement (p. 623) that “in 
