146 The American Geologist. March, 1901. 
ments apply to the earth as a whole, and not to its crust ; they 
deny the fluidity of the interior of the Earth, and do not pro- 
deny the fluidity of the interior of the earth, and do not pro- 
hibit any local deformations of the exterior crust. The once 
prevalent astronomical belief in the absolute invariability of 
the earth's shape and in the absolute fixity of is axis of rota- 
tion (expressed, e.g., by Sir J. Herschel in 1862) no longer 
hinders progress. In fact, astronomers tell us that, instead 
of the absolute fixity of the pole, it now shifts its position to 
an appreciable extent under the influence of the movements of 
the atmosphere, the unequal melting of the polar ice, and by 
heavy falls of snow on the Siberian highlands. These move- 
ments of the pole are important, because they are taken to 
prove a certain elasticity in the earth. The movements dem- 
onstrated by actual observations are so far minute; but they 
at least allow geologists to say that, as such slight causes as 
those mentioned produce appreciable effects, more powerful 
causes acting for longer periods would work greater changes. 
Summary. 
The object of the paper is to show that the old belief in a 
definite plan of the earth is j.ustified, since the distribution of 
land and water on the globe has been determined by the tetra- 
hedral arrangement of the elevations and depressions in the 
surface of the lithosphere. 
This tetrahedral plan is shown by the existence of (i) a 
northern land-belt, surrounding a northern ocean, and giving 
off three meridional land lines, which taper southward ; (2) the 
southern ocean belt surrounding a south polar continent, and 
the three meridional oceans; (3) by the antipodal position of 
land and water; (4) by the course of the main watersheds and 
mountain chains. 
It is held that this arrangement was not established in the 
earth's infancy, and therefore has to be attributed to some 
agency which has acted throughout geological history. 
There are reasons for believing that a contracting sphere 
with a hard crust would undergo tetrahedral deformation, and 
the evidence of geodesy shows that the earth has been de- 
formed from its spheroidal form. Its present figure may be 
defined as a geoid, which has been derived from a spheroid 
by irregular tetrahedroid deformation. 
