The Plan of the Earth and its Causes. — Gregory. iiy 
But of course in the earth the faces are not flat, but are 
convex. If the flat faces be replaced by projecting pyramids 
with curved faces, so that the form is globular, the arrangement 
of land and water remains the same, but the shore-lines are 
more complex. Green has shown what the shapes of the land 
5c 
FIG. 5. 5a, DIAGRAM OF A SIMPLE TETRAHEDRON. 5b, DIAGRAM 
OF A TETRAHEDRON WITH A SIX-FACED PYRAMID WITH CON- 
VEX FACES ON EACH OF THE FOUR FACES. — 5C, THE TRACE OF 
THE TETRAHEDRAL EDGES ON A SPHERE; THE THICK LINES 
SHOW THE POSITION OF THE TETRAHEDRAL EDGES. 
and water areas would be in such a tetrahedron. The re- 
semblance between his diagrammatic continent and Africa and 
S. America, and between his ocean and either the Pacific, In- 
dian ocean, and S. Atlantic, is very striking. 
THE TETRAHEDRAL COURSE OF GEOGRAPHICAL LINES. 
The agreement between the facts of geography and the 
tetrahedral theory goes further. The four faces of a tetrahe- 
dron meet along six edges, which should be lines of elevation 
on a globe. The trace of the edges of a tetrahedron on a sur- 
rounding sphere forms a circle in the northern hemisphere, and 
three ' 'm ' or meridional edges meeting at the south pole. 
