138 The American Geologist. ^arch, looi. 
geographers and geologists, the insistence on this deformation 
may not be useless. It may be worth while adding a quotation 
from Prof. C. A. Young,* to show that the spheroid of refer- 
ence is only a convenient assumption. "On the whole," says 
Prof. Young, "astronomers are disposed to take the ground 
that since no regular geometrical solid whatsoever can absolute- 
ly represent the form of the earth, we may as well assume a 
regular spheroid for the standard surface, and consider all var- 
iations from it as local phenomena, like hills and valleys." 
As deviations from the assumed spheroid of reference exist, 
it remains to inquire whether there is any evidence that they 
agree in position and arrangement with the theory of the tetra- 
hedral deformation of the lithosphere. 
The evidence already quoted of the dissimilarity between 
the northern and southern hemispheres and the elongation of 
the latter, is geodetic proof of the northern flattening and the 
antarctic projection, i. e., of one face and one tetrahedral cor- 
ner. 
The three flattened lateral faces and three projecting verti- 
cal edges are sufficiently demonstrated by the three great 
oceans and the land-lines that have divided them. Practicallv, 
all the theories agree upon that point. Jt is well known that 
gravity is greater than was expected at most oceanic islands. 
Lallemand and de Lapparent have suggested that this is due to 
those islands being below the level of the ordinarily accepted 
figure of the earth, and therefore nearer the earth's centre of 
gravity.! Fisher has suggested that the Pacific ocean is the 
hollow left by the loss of the material which forms the moon. 
Faye has explained the ocean basins and the greater density 
of the crust below them as due to more rapid refrigeration 
below the cold oceanic abysses. According, therefore, to Faye, 
the rocks below the oceans contracted more than those below 
the continents, became denser, and accordingly sank. 
Thus from all points of view the three oceans represent 
areas of depression, and the three land-lines of South America, 
Africa, and Australia mark intervening projections. The 
oceans mark the low areas in the lithosphere as obviously as 
• C. A. Young, General Astronomy,' p. 101. 1889. 
t This explanation is inadequate, as it does not explain the deviation of 
the pendulum on coast-lines towards the ocean. The excess vertical attraction 
of the islands has been explained as due to the attraction of the mass of the 
island and its base. 
