80 REVIEWS 
as it has been used in geological literature.”” The language used in the 
Report was not intended to give the impression stated in the words just 
quoted. The writer, being aware that the word ‘“‘isostasy’”’ has been 
frequently misunderstood and used inaccurately, carefully defined it at 
considerable length in both his preliminary statements before the Wash- 
ington Academy and the Geodetic Association. The idea of a crust 
composed of relatively rigid material, floating upon a liquid or viscous 
substratum, is not necessarily implied in these definitions. Nor is it 
necessarily implied in the original definition of isostasy by Dutton.t The 
floating crust represents one possible method of isostatic adjustment. 
Dutton does not believe in a floating crust, nor does the writer. The 
geodetic investigation under discussion contains strong evidence, not set 
forth fully in either preliminary statement because of lack of space, which 
is against the crust hypothesis. The condition of approximate equilibrium 
called isostasy may exist in materials in which there are no sudden changes 
in viscosity. 
In his review Professor Chamberlin states that, under the accretion 
hypothesis, an initial arrangement of densities might be produced such that 
the condition of approximate equilibrium called isostasy would exist, and that 
therefore the present existence of isostasy does not necessarily prove any- 
thing in regard to the rigidity or lack of rigidity of the earth. The follow- 
ing quotation? shows that the writer recognizes that such an initial con- 
dition may have existed, but that he also recognizes that, even if it did 
exist, the present facts still constitute a proof of low rigidity and of iso- 
static readjustment: 
It is possible that the continents and oceans are in their present positions 
because light materials accumulated at the outset in the places now occupied 
by the continents, and heavier material accumulated where the deep oceans 
now lie. This would constitute an initial isostatic adjustment. But the geologic 
evidence is overwhelming that within the interval covered by the geologic record 
many thousands 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 at 
present. 
The writer believes the degree of completeness of the isostatic adjust- 
ment to be a measure of the degree of effective rigidity, under forces con- 
1 C. E. Dutton, ‘On Some of the Greater Problems of Physical Geology,” Bul- 
letin of the Philosophical Society of Washington, Vol. XI, p. 53. 
2 Hayford, The Geodetic Evidence of Isostasy, p. 35. 
