26 
GEOLOGY: W. BOWIE 
Proc. N. A. S. 
balance, the column under an area of sedimentation should be too light 
and that the column under an area subjected to long erosion should be 
too heavy. 
The writer's conclusion has been confirmed by a recent investigation 
in India. 4 
If the columns under the Cenozoic and the Pre-Cambrian formations 
are in isostatic equilibrium, then there must exist the compensation not only 
of the material which is above sea level but of the deficiency of matter in 
the Cenozoic and the excess of matter in the Pre-Cambrian material which 
exist below sea level. 
It is inconceivable that 20,000 or 30,000 feet of sediment all deposited 
at a low elevation, approximately sea level, could take the place of an 
equal volume of material presumably of normal density and still have the 
column contain normal mass, without there having occurred an increase 
in density in the material of the column to balance the deficiency of mass 
in the volume occupied by the recent sedimentary material. If the 
Cenozoic material is 30,000 feet thick, the deficiency in mass is about 3000 
feet, and the isostatic compensation will be equal to this amount. In 
the 75-mile column the increase in density necessary to balance the Cenozoic 
deficiency will be about 3 /± of 1%, if we assume that the average density 
throughout the column is approximately three. If the density is greater 
than that, the percentage will be proportionately increased. 
In order to maintain the isostatic balance a mass equivalent to 27,000 
feet of Cenozoic material must have been transferred from the column under 
the Cenozoic formation. 
The contraction of the material in the column under the Cenozoic forma- 
tion may have begun before sedimentation was initiated, but further con- 
traction and consequent increase in density must have taken place with the 
sedimentation for, otherwise, the surface of the column would have stood 
at some times much above sea level, which seems to have been improbable. 
The evidence available from geodetic investigations indicates in the 
strongest way that land masses are in equilibrium and that this equilibrium 
exists in comparatively small areas. A natural inference is that land 
masses have been equally in equilibrium in former geologic periods. 
How, then, can an area of sedimentation at approximately sea level, 
of one age, be a mountainous area in a succeeding one? 
Mountain formation by transportation of material horizontally from 
one column in equilibrium to another column in equilibrium could not 
take place without destroying the isostatic balance. Of course, material 
is transported from one column to another (surface transportation after 
erosion is not included in this statement) but this is when the columns are 
out of balance and the movement renews the isostatic equilibrium between 
the two columns. Mountain masses are not excess loads on the earth, 
as is proved by the existence of the isostatic conditions in mountainous 
