384 THE FLAN OF THE EARTH AND ITS CAUSES. 



great equidistant corner stones, the Archaean blocks of South Africa, of 

 Australia, and of Patagonia and the Patagonian platform. 



What the South Pole was doing then is hidden by our deplorable 

 ignorance of that area; but there is evidence that to 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 Bering Sea and 

 North Atlantic belong to two essentially distinct faunas. But in Upper 

 Paleozoic-Triassic times one fauna occupied both regions, and that 

 fauna moreover extended uninterruptedly round the Northern Hemis- 

 phere, and apparently, along certain lines, extended some distance to 

 the south. There was, in fact, a northern ocean belt, which apparently 

 surrounded a cold arctic land. The distribution of land and water 

 was then on the same plan as at present, but with land and water 

 exactly reversed. There were two opposite interlocking belts of land 

 and sea, the former based on three Archaean corner stones, the latter 

 projecting toward the equator between three Archaean plateaux. 



Thus the plan was the same as at present, but the conditions were 

 reversed. This gives us the clue to the mountain chains of the same 

 period. That, also, was a double system. There was a subtropical 

 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, opposite the three coigns, we have three mountain ranges 

 running along the meridional edges. These are the Ural Mountains 

 (60° E.) north of the eastern continuation of the South African coign, 

 the Appalachians (80° W.) north of the western 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 begun would be strengthened by 

 every fresh contraction. But owing to the world's rotation, the tetra- 

 hedral collapse is steadily resisted, and confined within narrow limits. 

 The deformation formed by one period of slow, quiet contraction may 

 be lost on the restoration of equilibrium at an epoch of great crustal 

 disturbance. When deformation begins again, in consequence of 

 renewed contraction, the flattening may occur elsewhere. 



This hypothesis of the alternation of periods of deformation with 

 periods of spheroidal recovery is geologically useful, as it suggests 

 an exydanation of a certain periodicity in geological phenomena. For 

 instance, the latter half of Paleozoic time may have been a time of slow 

 tetrahedral collapse, culminating in an instability which led to the 

 great mountain movements which closed the Paleozoic; then followed 



