Vol. 7, 1921 
GEOLOGY: W. BOWIE 
27 
regions, therefore the materials forming the mountains were not moved 
horizontally to the region. We are forced to the conclusion that the 
mountains must result from vertical movements in the columns under 
them. The vertical movement evidently must be due to an expansion 
and consequent decrease in density in the material of the column. 
When we consider that all extensive areas of recent sedimentation on 
which we have gravity stations are in isostatic equilibrium and that 
mountain systems formed in previous sedimentary areas are also in equi- 
librium, we have no alternative to the view that an actual expansion of 
the columns under the mountains has taken place. 
The objection will be raised that there is abundant evidence that there 
have been horizontal movements in the materials forming the mountains. 
This is granted but is it necessary to go far beyond the mountain area 
for the forces acting laterally which cause the observed horizontal move- 
ments? Can we not conceive that, in the uplifting of the mountains of 
the Appalachian and Himalayan systems, for instance, the vertically 
acting forces will cause the material to progress in the directions of least 
resistance and that these directions may be horizontal in some cases 
and in others at varying angles with the vertical. 
During the period of sedimentation, material probably was not laid 
down in smooth concentric sheets but in irregular ways. In the process 
of uplift, due to expansion, the rate of expansion would undoubtedly be 
different in different parts of the zone. The sediments are of varying 
thickness, the material on which the sediment had been deposited varies 
in composition and consequently in its resistance to uplift, and finally 
there is cubical expansion of the material which must cause the material 
at the borders, but outside of the columns, to modify somewhat the up- 
ward movements of the expanding mass. At least this effect must be ex- 
erted near the upper part of the expanding column. The areas affected 
are not small for the area of the base of the Appalachian system is more 
than 1000 miles in length and is approximately 200 miles in width, on an 
average. Consequently, there seems to be sufficient space for the develop- 
ment of lateral movements within the area due to local causes. 
The drowned valleys along the continental coasts show that decided 
subsidences have taken place. How could these have been caused ex- 
cept by contraction of the columns under the affected areas since the 
pendulum proves rather conclusively that the regions along the coasts are 
in isostatic equilibrium? Here the reverse process to that of mountain 
forming operated. 
The writer has arrived at the conclusions here presented after endeavor- 
ing to harmonize geodetic data and certain observed geological facts. 
He makes no attempt to formulate a theory as to what agencies are at 
work to change the density of material far below sea level (but within, say, 
75 miles of the surface), but he suggests that the vertical movements ac- 
