36 THE OCEAN RIVER 



to but thinner than that of continents, are no longer unchal- 

 lenged, for Rothe brings forward evidence from seism ological 

 records to show that earthquake shock waves travel more rap- 

 idly in the western bed of the ocean than in the eastern part. 

 These waves travel faster in the heavier types of rock; thus it 

 appears that the western part of the Atlantic is floored by the 

 same heavy basalt rock which underlies the Pacific, whereas 

 the eastern half has a granite foundation, and is more like the 

 continents. 



Explorations made by Ewing, Tolstoy, and others aboard 

 the research vessel Atlantis in co-operation with the National 

 Geographic Society during the past two or three years, only 

 partially support Rothe's ideas. Most interesting perhaps was 

 the discovery that the Ridge is carved into valleys, and that in 

 these valleys are extensive flat terrace-like plains. They bring to 

 mind the smaller terraces characteristic of valleys exposed to 

 the air. They are unlike river valleys, however, and more needs 

 to be known before we may draw any definite conclusions. 

 On the other hand, it was also discovered that over 4,000 

 feet of sediment rests upon the slopes of the mid-Atlantic 

 Ridge, and this suggests a considerable period of submer- 

 gence. Another surprising haul from the deep ocean bed 

 between Woods Hole and Bermuda showed the presence 

 of coarse sandy material. Sands of this kind have been until 

 now considered typical of shallow waters near shore, and the 

 startling discovery of such material in deep offshore water will 

 at least bring about a considerable revision of our ideas, al- 

 though it fits in with what is now known about the deep can- 

 yons which extend outward from the land along the seafloor. 



Although modern submarine investigations have not proved 

 anything conclusively, they have begun to obtain new evi- 

 dence from the relatively young science of marine geology. 

 A new period of interest and accomplishment in undersea 

 exploration has begun, and the spirit that activated Columbus' 



