DIASTROPHISM AND THE FORMATIVE PROCESSES 529 
as such. It is merely convenient for use in forming a concrete 
conception of the work of deformation taken in its largest sense. It 
is my belief, however, that the ratio of protuberance to depression 
as defined by the sea-level has not radically changed from the 
beginning of the Paleozoic to the present time, but geologists enter- 
tain varying opinions on this point. 
It is becoming more and more clear as study proceeds that the 
great deformations that determine the ocean depressions and the 
continental protuberances are not mere superficial incidents of the 
earth’s development. One of the latest geodetic inquiries into 
the distribution of gravity finds that the outer part of the earth in 
the United States reaches a state of isostatic equilibrium only at a 
depth of seventy odd miles, even when an extreme hypothesis of the 
distribution of differences of specific gravity is made the basis of 
interpretation.’ If a natural dying away of the differences of 
specific gravity from the surface downward is made the basis of 
interpretation, the depth is much increased and may be more than 
doubled. The geodetic data of India, a land of great deformations, 
seem to demand much greater depths than the data of America.? 
Considerations that lie in the mechanics of the case strongly support 
the view that the portion of the earth that is involved in the highest 
order of deformations is both thick and stiff. 
Now in the deforming of a spheroid whose yielding parts are 
so deep and stiff as to take on and maintain broad inequalities like 
the continents and oceanic basins, certain mechanical methods are 
inherent and inevitably express themselves in the resulting con- 
figurations; for example, the portions that are most nearly horizon- 
tal will in the nature of the case be those at the bottoms of the sags 
and the tops of the swells. These portions may be nearly tangent 
to horizontal planes, but the dips of the intervening surfaces will 
naturally become increasingly greater toward points midway 
between the swells and sags, or at least somewhere between them. 
If, therefore, the sea-surface lies at such a position that one-third or 
1 John F. Hayford, ‘‘The Figure of the Earth and Isostasy from Measurements in 
the United States,” U.S. Coast and Geodetic Survey, Washington, D.C., 1909. 
2G. S. Burrard, “‘On the Origin of the Himalaya Mountains, a Consideration of 
the Geodetic Evidence,” Prof. Paper No. 12, Survey of India. Calcutta, 1912. 
