The Plan of the Earth and its Causes. — Gregory. 143 
the south of this southern land-belt there was a cold, ice-laden 
sea. 
Now let us consider the state of affairs in the arctic regions 
at the same period. At the present time the Mollusca of the 
Behring sea and North Atlantic belong to two essentially dis- 
tinct faunas. But in upper Palseozoic-Triassic times, one fauna 
occupied both regions, and that fauna moreover extended un- 
interruptedly round the northern hemisphere, and apparently, 
along certain lines, extended some distance to the south. There 
was, in fact, a northern ocean-belt, which apparently sur- 
rounded a cold arctic land. The distribution of the land and 
water was then on the same plan as at present, but with land 
and water exactly reversed. There were two opposite inter- 
locking belts of land and sea, the former based on three Arche- 
an corner-stones, the latter projecting toward the equator be- 
tween three Archean plateaux. 
Thus the plan was the same as at present, but the condi- 
tions were reversed. This gives us the clue to the mountain 
chains of the same period. That also was a double system. 
There was a sub-tropical mountain girdle, the ruins of which 
we can trace right across the old world from eastern China 
to western Europe, where it is cut off by the Atlantic slope. 
And projecting meridionally from that equatorial girdle, op- 
posite the three coigns, we have three mountain ranges run- 
ning along the meridional edges. These are the Ural moun- 
tains (60° E.) north of the eastern continuation of the South 
African coign, the Appalachians (80" W.) north of the west-' 
ern part of the old Patagonian coign, and the old broken axis 
of Kamtschatka (160'^ E.) north of the coign of Australasia. 
Deformation and Recovery. 
Such a change in the position of the flattened faces is by 
no means improbable in the case of a revolving globe. In the 
case of a stationary body, a tetrahedral deformation once be- 
gun would be strengthened by every fresh contraction. But 
owing to the world's rotation, the tetrahedral collapse is stead- 
ily resisted, and confined within narrow limits. The deform- 
ation fonned b>- one period of slow, quiet contraction may be 
lost on the restoration of equilibrium at an eix)ch of great 
crustal disturbance. When deformation begins again in con- 
