14 EARTH FEATURES AND THEIR MEANING 



contract though the outer shell is no longer able to do so. The 

 superficial area being thus maintained constant while the volume 

 continues to diminish, the figure must change from the initial one 

 of greatest bulk to others of smaller volume, and ultimately, if the 

 process should continue indefinitely, to the tetrahedron, which of 

 all regular figures has the minimum volume for a given surface. 



That a contracting sphere does indeed pass through such a 

 series of changes has been shown by the behavior of contracting 

 soap bubbles and of rubber balloons, as well as by experiments 

 upon the exhaustion of air contained in hollow metal spheres of 

 only moderate strength. In all these instances, the ultimate 

 form produced indicates an indenting of four sides of the sphere 

 which have the positions of the faces of a tetrahedron. The late 

 Professor Prinz of Brussels secured some extremely interesting 

 results in which he obtained intermediate forms with six angles, 

 but unfortunately these studies were not prepared for publication 

 at the time of his death. 



The earth's departure from the spheroid in the direction of the 

 modified tetrahedron is, as we have seen, no hypothesis, but ob- 

 served fact revealed in (1) the concentration of the land about 

 a central ocean in the northern hemisphere; in (2) the antipodal 

 relation of the land to the water areas, and in (3) the threefold 

 subdivision of the surface into north and south belts by the two 

 greater oceans and the Caspian Depression. 



The earlier figures of the earth. The manner in which conti- 

 nent and ocean are dovetailed into each other in an east-and-west 

 direction has been generally adduced as additional evidence for 

 the tetrahedral figure as above described. Closer examination 

 shows that instead of being in harmony with this figure, it indi- 

 cates a departure from it, and, as we shall see, a significant depar- 

 ture which undoubtedly has its origin in the earlier history of 

 the planet. The mediterranean seas of both the eastern and the 

 western hemispheres likewise interfere with the perfection of the 

 tetrahedral figure and require an explanation. 



Let us then examine in outline the past history of the world 

 with reference especially to the evolution of the continents and 

 to the times and the manners of surface change. It is how well 

 known that there have been three major periods of great deforma- 

 tion of the earth's shell. The first of these of which we have 



