SHIFTING OF THE SOUTHERN CONTINENTS 77 



duce stretching, torsion, and blockwise sinking along this coast, and ex- 

 plain many of the peculiarities of the east coast of Asia and America, 

 the deep ocean bottoms, the rias coasts, the deep " graben " like the Fossa 

 Magna of Japan, and the down-faulted blocks which preserve the Trias 

 of the Atlantic coast. 



On the other hand, on a western coast the rising land moving west 

 and sinking sea moving east would tend to approach each other, and 

 this would add itself to the direct landward mountain- making thrusts 

 which were active along this coast. Moreover, the tidal stresses, which 

 will be discussed below, would combine with the forces here invoked to 

 cause the crumbling down of the eastern coasts and the upfoldings along 

 the westward ones, along all northeast and northwest lines. 



My colleague, Professor A. L. Kimball, has made for me the calcula- 

 tion that in an ocean 500 miles wide a sinking of the bottom one foot 

 per second would produce an eastward force of only 1,080 pounds to the 

 square foot per second ; a sinking of one foot per minute would produce 

 a force of 18 pounds per square foot per second, and so on. This is a 

 force so small that it may apparently be neglected except under most 

 favorable circumstances. 



Part II. The Zone of the Intercontinental Seas 



SUGGESTIVE RELATIONSHIPS OF LAND AND SEA AREAS 



To an observer approaching the planet from the depths of space a 

 most striking thing would be the three great triangular elevated land 

 masses projecting south, the three great depressed oceans tapering north. 



If we add the Arctic ocean and the Antarctic continent, and consider 

 the antipodal arrangement of land and water, the tetrahedral disposal 

 of the mountain chains and of the main divides as shown by Von Tillo,* 

 and consider further the geodetic measurements and pendulum obser- 

 vations which make the earth taper at the south pole and emphasize the 

 lightness (that is, elevation) of the continents and the excess of gravity 

 (that is, depression) over the oceans, so that the ocean surface is in a cer- 

 tain sense a concave surface, sinking from the continental borders, and 

 note finally the central lines of volcanoes which mark lines of fissuring 

 down the centers of the depressions, we may say that the tetrahedral 

 plan in the evolution of the earth's feature lines is strongly suggested by 

 simple observation. It is imperfectly realized, to be sure ; but we may 

 use the tetrahedral idea as a working hypothesis, and deduce that as the 

 three continents have had a common origin, the three homologous medi- 



*Petermann's Mittheilungen, 1887. 

 XI— Bull. Geol. Soc. Am., Vol. 11, 1899 



