FIRE, ROCK, AND SEA 21 



If the underlying basalt had been completely solid at the 

 time, the great moon scar would have remained as a gigantic 

 Pacific Ocean basin, and the Ocean River of the Atlantic 

 might never have come into existence. As it was, it is supposed 

 that the centrifugal effects of the earth's rotation began to pull 

 the masses of granite toward the equator over the still semi- 

 fluid basalt and then to separate them, as shown in the dia- 

 gram. A striking fact that supports this belief is that the 

 outlines of the present-day continental masses of Africa, North 

 and South America, Eurasia, Australia, and Antarctica are so 

 shaped that they fit together almost like the pieces of a jigsaw 

 puzzle. 



As the continents pulled apart the Atlantic basin was finally 

 formed. Earlier seismological research appeared to confirm 

 this by the discovery that whereas the floor of the deep Pacific 

 basin is composed of basalt, that of the Atlantic has a partial 

 layer of granite. This is thinner and less complete than the 

 granite floor of the continents, and could well have been left 

 in the gap as the continents drew apart, particularly since at 

 this time the lower layers of granite must have been soft and 

 plastic. Today there is doubt as to whether there exist any 

 substantial amounts of granite beneath the Atlantic seafloor. 



It may be that in some such way as this the moon's birth 

 caused the breaking up of the granite crust and its separation 

 to form the bed of the Ocean River. Since none of the present 

 continents possesses any rocks which could possibly have origi- 

 nated in the deep sea basins, some scientists are sure that there 

 has been no change in the relative positions of continent and 

 deep ocean since the basins were first formed. But there have 

 been many changes in the shape of the shallow ocean borders, 

 and equally great changes in the course of the Ocean River 

 itself. Ocean currents today have nothing in themselves to tell 

 of their past history, so that we are compelled to return to the 

 geologist in our attempt to follow the many different courses 



