8 Tlie American Geologist. January, 1900 
southern peninsulas. The explanation is supplementary to the 
presence of the tetrahedron, as propounded by Mr. Green. 
The tetrahedron rotates around the polar axis. At first the 
dift'trent points moved with equal velocities; but when the 
protuberances became accenuated the three upper ones were 
retarded, while the regions south of the equator moved more 
rapidly. Thus the hextetrahedron has been submitted to tor- 
sion, which has produced a line of continuous rupture near 
the equator corresponding to the well known volcanic belt or 
earthquake zone. Hence, it is easy to understand why the 
lines of elevation have failed to correspond exactly to the 
tetrahedral angles. Borrowing the language of crystallogra- 
phy, if the whole earth is a hextetrahedron. the line of rupture 
is a twinning plane, not necessarily coincident with any ele- 
ment of the crystal. The position of this plane is further 
justified by referring to the tides produced in the primitive 
earth while the crust was still thin. 
The equatorial bulge of the earth is. imderstood to pro- 
duce the precession of the equinoxes. As the three northern 
protuberances must have some effect for similar reasons, Mr. 
Green finds it in the inclination of the ecliptic. 
M. de Lapparent. in adopting this theory, finds in it the 
explanation of the excess of the attraction of gravitation in the 
northern hemisphere. The sea is attracted by these three pro- 
tuberances: but in the middle of each of the oceanic depres- 
sions the surface of the water would tend to flatten, as the 
latter is nearer the center of the earth. 
In studying the collapse of spherical bodies, Mr. Green 
quotes from experiments of Mr. Fairbairn. [Useful informa- 
tion for engineers]. Hollow glass spheres were reduced to 
fragments, and nothing could be learned as to the method of 
their collapse. Rubber spheres immersed in water tend to- 
wards a tetrahedron. Soap bubbles in the air present a slight- 
ly tetrahedroidal form when compared with air bubbles in 
water. Some organic bodies, like nuts and tetraspores, ex- 
hibit shapes indicative of a collapsing tetrahedral body. Cylin- 
ders show very satisfactorily a flattening from three dififerent 
directions after collapse. 
The sphere of all regular solids embraces the greatest vol- 
ume with the smallest surface. The tetrahedron has greatest 
